When we were first separating, I deluded myself into thinking maybe we could make the bird's nest thing work, where the parents move and the kids stay in the house...hah! I couldn't live with the man for a reason, KWIM?!!!! I think it would be nice for the kids to have the parents close, but I wouldn't live right next door to my ex. I don't need to explain every guest I have over, every choice I make, etc., which he would definitely nit pick on.
The same apartment complex could work so long as they are not adjacent apartments, both for noise and so you aren't constantly running into each other when coming and going, and maybe even if they are different floors or different entrances, for the same reason.
I would be uncomfortable to think of my ex knowing my daily routine, etc. I would love to live somewhere the kids could bike to my ex's house from mine someday in the future, but that is as close as I would likely get.