Our foundation is shared with the house attached to us. 

I know someone who had major structural issues with their foundation, got it fixed and was told by the lawyers that they didn't need to disclose it when they sold the house (they did disclose it).

Could I hire someone to do the foundation, utility connections and framing, then do the rest myself to save money?

I poured the foundation myself using quickset cement ($30 plus my time).

I understand that notes is a business best learned by doing, but I am trying to lay a good foundation of knowledge as a starting point.To date, I have read these books:"Invest like a Bank" by Beaux Blast" Little Green Book of Note Investing" by Fred Moskowitz"Real Estate Note Investing" by Dave Van Horn"Note Investing Made Easier" by Martin Saenz"Invest in Debt" by Jimmy Napier"Profiting from Non-performing Mortgage Notes" by Amed HazelI welcome any thoughts or recommendations that the group may have.   

Few things with MH that need to be assured is "Double wide" which you covered, On a permanent foundation/concrete slab, Not on axles/remove, Not moved from another property or living location, and built after June 1976 (Some investors require within 25 years). 

I am a "Foundation" Big Dog which is the lowest level that anyone can join at.

It's a favorable rate, and given the equity you have in your property, you have a good foundation for securing additional funding without compromising this rate.Considering your property is now an investment, and you're looking into financing options for updates, a VA loan could still be a viable path for you, even in your current situation.

The dig out is not horrible, but you will need to dig some test pits to see how far you foundation goes.

I'm looking for some rule of thumb numbers to understand the costs.Price LF  Footings:Price SF Slab Break and Replace:Price CY excavation:Price Block or SF - Block Foundation Walls:Assume a 5 stage underpin as well.