The two biggest things to consider are, of course, the power of two textures and limited shader use. I had a loading lag on the edge of when something came on-screen that had a shader on it. I just found another way around it and that solved that. Also, tiled backgrounds are neat and all, but you can get the vram way down with the chunks you mentioned you were going to do. If you have a lot of graphics, the higher VRAM use is fine, just try to not go overboard.
I'm not posting it as any means of showing off, but rather giving an example. It's pretty well optimized on graphics, though could probably use a little more. And there are no tiled backgrounds because nothing really repeats:
<img src="http://www.adamprack.com/blight/screenshots/trees.png" border="0" />
That layout is around 95MB of VRAM. There's a ton of motion going on (the grass and many of the pine needles blow in the wind), and a lot of objects. But without sticking to power of two, that would end up being a nightmare to run. Your graphics look fantastic, don't get me wrong. And I do have layouts that go up to around 125MB, but optimizing will allow you to get a LOT more detail on-screen without taking a hit.
In your case, those large wall textures could easily be tiled backgrounds and then post an occasional crack or whatever as a sprite over top to make sure it doesn't get too monotonous. Then you could use a mask layer for your lighting (search it on the forums if you aren't familiar) and then post your windows/etc. as sprites over that tiled background. Your interior levels lend themselves well to doing this.