Yes the mattress does bunch up against the dresser when the slide is in but flattens back out with the slide out. No big deal and doesn't hurt a thing.
Yes, but he was wanting to put a 80"mattress in place of the standard mattress. 5" would make a huge difference. Ours does not bunch up, but just touches. We sleep on it all the time with the slide in at Wal-Mart. I am still not sure what length I have after looking at my photo, but will actually measure it when I get it back.