My concerns are: -Some of the electrical isn't wired properly (double tapped)-furnaces 50+y old -various locations of water supply line show signs of leaks at some point-galvanized steel pipelines.

All electric.

There is no way to completely separate it from the main part of the house, as it also has the laundry machines, furnace, electric panel, and storage areas I need to access.

FHA 203(k) loans may be used for home purchases and renovation projects, such as installing roofing or flooring, bringing a property up to code by repairing health or safety hazards, or replacing plumbing or electrical systems.

The property I'm looking at is just over 7 acres, rural, has septic, water and electricity in place. 

Check roof/electrical/foundation/attic.

The more you have to take care of, the less time and energy you have to create more.

If advertised as 1600 feet which includes the 150+ of garage then the seller lied.I'm assuming the conversion appears to code, is insulated and electrical looks professional. 

This was a bit of a rude awakening for me. i had planed to do all the renovations myself but even though I was the owner I was not allowed to do plumbing or electrical as it is a "Commercial Building" and they needed licensed contractors for those two parts.

#2 - I have several contractor connections within the state including electrical, plumbing, construction, masonry and roofing.