Like I said above I don't see why we need to use sandstone, I feel like sandstone has been used quite a lot already.The sandstone block states are free in the URPS iteration of the Eriador RP hopefully being introduced with the 1.13 update so we could have a new texture for old sandstone.
On the topic of mixing textures, I think the white bricks can't be used for walls in any of these buildings. Not only because they are way too perfect but also because according to some source I stumbled upon during my quick research yesterday the only white rock they used was marble and that was only used for columns and statues. Especially the Byzantines tried to drive down the costs of building by increasing the thickness of the mortar layers between the bricks which resulted in warping and even collapse in some of their structures but at the same time established an important characteristic of byzantine architecture, the asymmetry/imperfection of their structures. The cost-efficiency they were striving for also means that they wouldn't have used marble, a much more expensive material, in their walls. One could argue that they might have been able to afford that in Lond Daer but I'd say white walls just aren't part of early roman/byzantine structures. Plus I can't imagine how you would ruin a white wall like that as marble gets a yellow tint over time.
About the byzantine style, we're only using it as a reference, obviously Numenoreans weren't exactly the same as the Byzantines, so we shouldn't copy them completely. Either way the concepts I made were for the richest, most fancy buildings (the palace complex) so they could most definitely afford marble in some areas.
Using block variations will always be needed. It'd be nice to have more possibilities though.really like the ruined concept. But I find it unfortunate that we are forced to use the stone texture to add some variation. I know it's been used in the past to simulate plaster which normally works in my opinion. However, according to the same source plaster facades were rather uncommon as the focus lay on making the interiors as fancy as possible. Maybe coming up with another texture for variation within large surfaces would help with making these walls look interesting while keeping consistent in where we use certain textures and what they are supposed to portray. If you have an idea send me suggestions and inspiration pictures!