As far as I know every placed block survives lava though the redstone itself doesn't if you have a leak as I found out to my dismay. I think a 2 wide bridge the best you could manage with double piston extenders as I can't think of a way to power the middle ones. A single piston would be easy to make as big as required but wouldn't look quite so good. I think I need to play around with some slime blocks and maybe a piston feed tape style is a better idea that coming out the floor.
Yeah I can take a look around for something, I think it is safe to assume we will need a reasonably big area so will try to find somewhere that wont require too much digging, de-forresting etc.
Does anyone have ideas for a rough design? More specifically what blocks we should use for the build? I'm thinking this as we will need a lot of blocks - to give some idea of numbers I think my current house is about 5 or 6 double chests of stone which is around 15,000 - 20,000 blocks, probably about the same in wood, a double chest or marble etc. I would assume a communal build is going to be bigger than my house so yeah, A LOT of blocks. The best builds seem to stick to 3, 4 or maybe 5 different blocks and if we can decide on them I can set up a few energy condensors as soon as I find a suitable area.