Concerning Vault City: it's stated that on at least one occasion, the raiders funded by Bishop had disabled at least one turret and had a clear shot into the city. As far as I could tell, the only reason they didn't have their way with VC is because Bishop didn't want them to (and, to be sure, it would've been a Pyrrhic victory at best.) Just sayin, VC != as safe as people think. I'd set up shop in the vault itself, or possibly V13 -- since it's always purged in vanilla FO, you get to establish your own Vault community!
Edit: Oh yes, and VC would be only if I had assassinated Lynette (without being suspected), or become Captain of the Guard -- which is ridiculously hard to do, by the way.