Thomas,
I'm also going to take the full time route. I'm going to be a stay at home dad for the next few years which should provide me with plenty of time to cut the frame. I just wish I had your collection of tools to simplify the process!
How long has the farmland been in your family? Building my house wouldn't have been even a remote possibility if my parents hadn't recently bought 18 acres to retire on. They generously gave my wife and I one of the parcels (5.5 acres) to build on. While the center of the property was clearcut prior to the purchase, the land is probably worth twice as much as they paid just two years ago (7k/acre).
Going from ~2400 to ~900 sq ft is a big change, especially for a family of six. My wife and I continue to confound my parents and siblings as we moved from a 600 sq ft rental in Seattle to a 350 sq ft fifth wheel. Unfortunately, we made the move earlier than planned--we discovered the day after the purchase that we couldn't place the RV on our land, not even to store it!
Our house's final square footage will top out 1200 to 1300 which will feel like a mansion after the RV (which has just enough space for my wife and I, our son, and a dog).
As far as the straw bales go, they really are quite simple to work with when you're enclosing a single story home. Using bales on upper floors is possible, but would take up quite a bit of space. You'd probably be better served with a straw/clay mixture like Laporte's
econests if you have any energy left after finishing your house. You could always build a small workshop, playhouse, or cabin with your hay and a few more trees.
-Aaron
