It would probably be a lot easier to work with the moon we already have, and it wouldn't screw up things so much (and apart from the fact that it's already in place, it's also conveniently close).
There's plenty of water there, as long as we can thaw the polar ice, and we'd need to keep it in huge closed basins but that shouldn't be too much of a hassle. In fact the base that is to be established on the moon by 2018 and thereafter will need to do this. I'd say we'll have a living moon within a hundred years. If you wanna tow one from elsewhere, you'd have to go at LEAST out to Jupiter (since the Martian moons are slightly uninteresting and Venus and Mercury have no moons) and that would take, let's be optimistic, a couple of hundred years to figure out. Hypothetically speaking, of course.
