diy Coffee Bar

If you already have a nespresso machine, then I don't see the problem - they're not that different from keurigs really. Although, either way do be prepared for it to get jammed or broken - potentially drunk people trying to figure out how to use it (even with clear written instructions that a child could follow) are not always sensible!

I've been to weddings with these machines as the coffee option and they just never seem to work right for a crowd (run out of water repeatedly, have an error message, the whole table/display gets very messy fast).

I agree with maggie ^ you need someone to watch it enough to help refill water or at least have water nearby for the refill

This sounds better in theory than practice. You need to hire someone to be in charge of it all night. An alternative would be renting a large metal coffee maker and having creamers and sugar on the side.