How long are you looking to work on it before you sell it, or are you going to rent it for a while, then sell it?
If you've jacked up a house before and done the structural supporting work, then you know it's not for the faint hearted. No permits needed, building inspectors?
Glad you mentioned that you probably would need to do some roof repair, I was wondering how much damage the sagging caused.
Fireplaces add charm to a home, but rebuilding them isn't a minor expense, especially if they need a liner. Sounds like you've got some hefty expenses ahead - sheet rocking, painting, finishing, appliances, bathroom, laundry hook up, lighting, landscaping...and if you sell with realtor 6%. Only you can say if it's worth it.