Some interesting ideas here. PJ, you don't say how many people/pets will be living in this initial dwelling. A couple of years ago, just for grins, I designed an 8' x 12' house for one person (well, there was room for a second chair). Obviously, few people could live in such a dwelling for very long, but it would be possible for some.
My suggestions would be that you start by finding out exactly
what your local zoning laws are. Don't waste any time or money looking at anything until you know what you can and can't do.
Once you have that figured out you can work on where the main house will be and where the guest house will be. You will want them fairly close for the sake of utilities.
Assuming that local codes permit it, why not buy one of those fancier "sheds" (like this: Shop Heartland Estate Gambrel Engineered Wood Storage Shed (Common: 12-ft x 16-ft; Interior Dimensions: 11.42-ft x 15.42 Feet) at Lowes.com
) and set it up as a small house? That was the largest I found with one search of Lowe's, but I know there are larger ones. You could insulate it fairly easily. I suspect that you could build a pretty nice small house for your $10,000 budget - at a LOT less work.
BTW, Barth was a high-end MH back in the day and still has a following. A MH is designed to be driven, not permanently parked somewhere.