Backing up to the original posts - I'm late in joining in on this conversation -

Since you already own the land, pretty much anything you put into the house is going to be cheaper than building a new house. A lot of contractors will say it's not worth it, but from a builder's standpoint (paying labor), that's just
their opinion. New housing in my area costs $125 or more per square foot to build - eeek!
Since you can do so much of the work yourselves, I say GO FOR IT!
Your nose is the best way to see if there's mold, and it seems like there isn't. If there is some found later, you can fix it. You can fix a sagging roof. You can even have a cracked or bowed foundation fixed. But since the floors don't creak and are fairly level (?), it sounds like that's not a problem. I agree, new wiring and plumbing would be a good idea if you're gutting the house.
Judging from your pictures, it looks mostly cosmetic. And I echo some other posts, buy what you need when it's on clearance and scrounge.
We did it, and you can, too!