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.  

If my health was a rental property I'd say it's probably C class with sketchy tenants that mostly pay on time but sometimes have to be evicted, the roof needs reshingling and the foundation has some cracks that probably need some attention 🤣

Even a modest first investment can be a solid foundation for future endeavors.

Once you have this team in place, you should have the foundation to invest in any market confidently while not being there physically. https://www.biggerpockets.com/blog/core-four-real-estate-team

If you start before having both of those foundations strong, then things will go wrong.

Once you have this team in place, you should have the foundation to invest in any market confidently while not being there physically.I think Columbus is a great option to consider.