You have gotten a lot of good feedback from everyone on here. Back to your original question, I believe you can make it liveable in 3 months assuming you do not have to gut it and start over, and at least a few of your major systems are sound. We purchased a
1966 26' Overlander last year that had been sitting in a side yard for 20 years. It was work, but it really wasn't in that bad of shape considering. The floors were solid, no frame damage, but every other system needed addressed. I spent about a year on and off getting it to a solid usable shape, hunting for deals like a used DSI water heater, cheap new A/C unit with heat, and so on.
I like the idea of what you are going after, and I would definitely keep looking for the longest newest AS you can afford which would allow you to not have to dig in to deep to get it to a good spot and work for your family.
Good Luck, and post some pics when you find it!