All 3 of your pre-booked LL must be at one park. However, once you use your first pre-booked LL, as long as you have park hopper tickets, you can book another at any park with no tier restrictions.
It's possible, since there are no tier restrictions when getting LL day-of, but there are still questions on when that takes effect. 7 am? After you use your first pre-booked? We don't really know yet.
FP and G+ LL both expired at the end of the window as if you'd used it, so it seems like a safe bet that LL-MP will work the same way.
No official word on overlapping, but reliable sources are reporting a 15 minute overlap will be allowed.