<For Context: I asked these questions as part of the planning for the next misty mountains section>
Thanks a lot Eriol, also good idea to open a forum post about this. I will elaborate my conclusions here in a bit more detail than I did in the post about the project, for discussion.

1. Is "the High Pass" which Glóin takes the same road as Thorin's company's "a high pass"?
My conclusion is NO, but it's a connection of multiple small hints Tolkien gives in various places:

• In the Hobbit, Gandalf mentions that Goblin Town has an older entrance than the one the Company of Thorin entered through, which exits to a different pass which can be traveled one more easily, however the Goblins block it, hence they attempt the more difficult route. It would make sense that that other pass which is easier to travel by, is the one connected to the Great East Road, just because of the importance of that passage.
  
  Spoiler

  The Hobbit - Chapter 6: Out of the Frying-Pan into the Fire said:

  The wizard, to tell the truth, never minded explaining his cleverness more than once, so now he had told Bilbo that both he and Elrond had been well aware of the presence of evil goblins in that part of the mountains. "But their main gate used to come out on a different pass, one more easy to travel by, so that they often caught people benighted near their gates. Evidently people had given up going that way, and the goblins must have opened their new entrance at the top of the pass the dwarves had taken, quite recently, because it had been found quite safe up to now. I must see if I cant find a more or less decent giant to block it up again", said Gandalf, "or soon there will be no getting over the mountains at all."

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• Then of course Glóin's quote in Rivendell. The timing is very important here. The quote of Glóin is spoken in Ta 3018, 17 years before the server. He says that the lands east of the passes are now again under more firm control of the Beornings, which was not the case before the Battle of the Five Armies in TA 2941. So the pass that Glóin came by was not controlled by the Beornings in TA 2941, and it seems more likely to me that if they can choose which pass to restore they would pick the one most easiest to travel by, which would not be the one the Dwarves and Bilbo took. Theres 60 years between the Battle of the Five Armies and the point our server is set at, which would be enough time to restore the pass. Also, notably, Glóin does not mention any major difficulties when crossing the mountains - in the contrary, he implies that thanks to Beornings, its relatively easy and safe to take this route.
  
  Spoiler

  The Lord of the Rings - Book II - Chapter 1: Many Meetings said:

  Gloin looked at him. 'If you have not heard, I think we will not speak yet of that either. Master Elrond will summon us all ere long, I believe, and then we shall all hear many things. But there is much else that may be told.'
  Throughout the rest of the meal they talked together, but Frodo listened more than he spoke; for the news of the Shire, apart from the Ring, seemed small and far-away and unimportant, while Gloin had much to tell of events in the northern regions of Wilderland. Frodo learned that Grimbeorn the Old, son of Beorn, was now [>> RECENT CHANGE] the lord of many sturdy men, and to their land between the Mountains and Mirkwood neither orc nor wolf dared to go.
  'Indeed,' said Gloin, 'if it were not for the Beornings, the passage from Dale to Rivendell would long ago have become impossible. They are valiant men and keep open the High Pass and the Ford of Carrock. But their tolls are high,' he added with a shake of his head; 'and like Beorn of old they are not over fond of dwarves. Still, they are trusty, and that is much in these days.

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The passes surely are in the same area, only already because Goblin Town connects to both of them. On the other hand, they spend about three entire days in there, so Goblin Town is larger than Moria confirmed.

2. Is the Ford of Bruinen part of the Great East Road? aka does Rivendell lie north or south of the Great East Road?
I think you misunderstood the point of the question slightly, Eriol. The core question I actually wanted to solve was, where exactly the Great East Road (GER) leads through around the area of the Ford resp. Rivendell. That there is a continuous connection all the way through to the other side of the Misties is very clear. But I thought it could be that, the Ford only lies on a small side route which branches off the GER to Rivendell, or Hollin, and the GER itself always stays north of the Ford and never actually gets to it. At the point at which I posted the question, this was still not 100% clear to me, but in the LotR it specifies it very explicitly:
The problem I have is the following: I really really want to find a loophole so that I can put the GER going eastwards north of Rivendell (not south), because on our map there is no space to put it south of Rivendell (the High Moors are there, and right below that is already the Gladden Pass). The issue is, if the GER crosses the Bruinen, I would expect it to remain south of the Bruinen, otherwise it'd have to cross the Bruinen again, which seems oddly inconvenient. However, Rivendell lies on the Bruinen (Aragorn calls it "the Bruinen of Rivendell"), thus "south of the Bruinen" would mean "south of Rivendell". Even the Atlas is unsure about this it seems, it puts the Ford south of Rivendell, but the High Pass north of Rivendell. And of course the GER should not really run straight through the HIDDEN valley of Rivendell.

The problem at the core is, that our Rivendell is too close to the mountains. If it weren't it would have been less of a problem to lead the GER south around Rivendell.

So yeah, the Ford lies on the GER, but whether Rivendell lies north or south of the GER is unclear.

And just as I write this post I think I have found the most elegant way to solve the dilemma for MCME, without contradicting any single lore fact: Put the Bruinen underground, and make the road go above the cave. It may sound silly at first, but the longer I think about it the better I like the idea. There's many real life examples of rivers diesappearing into gullies and spouting up again a few kilometres further. I started looking into what rock types would be required for this, found it may be sandstone and yeah sandstone caves are a thing. But then I realize that I don't even need to research, Tolkien himself implies the possibility:

The Hobbit - Chapter 3: A Short Rest said:

There were gullies that they could almost leap over; but very deep with waterfalls in them.

Click to expand...

I mean I wondered so much, how can a place thats at the course of one of the largest rivers of Eriador remain hidden? Boom! Thats how!
#PutTheBruinenUnderground

3. Where does Thorins Company leave the Great East Road, where Frodo and Co.?
This is a question of lesser relevance, but in neither story there is a clear note on the point where the leave the "official" road to tread on the "secret" path to Rivendell which I found odd. It almost implies that if you follow the remainings of the GER that you'll somewhat automatically end up on that path to Rivendell which would be inconvenient...

4. In what condition is the Great East Road and the High Pass at the point of time the server is set at? (3001 TA)
This question is based on the description of the road in the Hobbit, where it seemingly grows very badly maintained after Bree. My interpretation is, that at the time of the Hobbit, barely anyone still used the road. There's nothing east of Bree before the mountains except Rivendell, and everything points to that traversing the mountains during the time of the Hobbit in that area is mostly a suicide mission, and barely a viable trading route. Mt. Gundabad is taken over by Orcs, Erebor by Smaug, Moria by the Balrog, all that remains are the Iron Hills and the settlements in the Blue Mountains. And with so many dwarven populations having fallen out of "business", and the number of orcs being as high as never before, trading most likely ceased altogether between the various dwarven populations. The lands of the Beornings are also put into defensive mode by the orcs, and Esgaroth has the additional hurdle of Mirkwood that keeps them off trading / traveling westwards.

My interpretion is that the Beornings start maintaining the High Pass after the War of the Five Armies, probably profiting from the lessened numbers of Orcs. However, the Orcs definitely don't abandon the Misty Mountains, as Frodo witnesses on Amon Hen. When the restore the High Pass it would only make sense to also maintain the Great East Road, to get a complete connection again. Maybe they could have been even cooperating with the Breelanders on that. Its 60 years they would have time for that. In the LotR there is no description that the road is in a bad condition (as it is mentioned in the Hobbit), so it may be possible that it was restored in the meantime. On the other hand, during the LotR Strider considers the road still very dangerous.

Oh and there's someone else who uses some pass near Rivendell between TA 3001 and 3018: Bilbo. In Rivendell, when he meets Frodo again he tells him that he visited Dale. And with his 111+ years the passage of the mountains can't anymore have been that hard as it was during the Quest to Erebor.

5. Does Thorins company leave Rivendell by the same way through which they entered?
For long I have had my mind set to that theres only one path to Rivendell. But two small details hint towards another one.

1. In the Hobbit it says that on their leave the dwarves "rode away" while the path they entered Rivendell on was described to be rather unsuitable to ride a pony on.
2. Gandalf entered Rivendell from the north.

The Atlas also suggests that the Company left Rivendell on a windy path northwards.

6. Why does the Fellowship of the Ring not consider using the High Pass nor the Gladden Pass as viable options for their journey to Mordor?
Same answer as Eriol. Too many Orcs, and required passing close to Dol Guldur. While Sauron may no longer be there, many Orcs and other evils surely still dwell there.

Yay and another 10k+ post down
Link to the Misty Mountains project post: http://mcmiddleearth.com/threads/misty-mountains-part-3-high-pass.5639

It'd just come so incredibly close to Rivendell, if it weren't for some trees, you could actually see the rooftops from the road...