She's not likely to go for you having full custody (there's a shame factor for women who lose custody of their kids) but a 50:50 custody arrangement will likely mean she won't actually TAKE her full 50% at the moment (since she's got to have free time for her midlife crisis carousing). I suspect if you end up with 50:50, you will actually have the kids more than 50% of the time.
Whoever moves out will still have to get a home with room enough for the kids, even if they're only there on weekends.
Are you sure YOU can afford the house? Many times the LBS wants to hold on to the old house for the sake of the kids - but just be sure that it is actually a sound financial decision for YOU.
