Also, does anyone know the ballpark amount that needs to be spent to develop 7.5 acres with infrastructure, plat the land, county water/septic hook ups, paved road etc. 

If you put mobile homes on a lot, you need to have water, electricity and septic (or sewer connection). 

I'm looking for your typical double wide or smaller house on a little plot of land with hopefully city water and no land or HOA fees.

A water line burst over the winter while we were away and we are stuck with a bill of 3500.

One of the houses had a active water leak with kitchen sink day 2 of my ownership. 

The garage itself is pretty dilapidated--old water damaged doors, a new roof, but many ad hoc repairs and some signs of rot.

I had an incident where the pipes froze and the tenants didn't have any hot water. 

I requested the seller fix the roof repairs (small fix), bathroom faucet leak, replace water heater (really old), and replace ac/furnace unit (old as well).There’s about 5 smaller things that I said I would fix. 

. - There are currently 22 full hookup lots (water, electric, and sewage) and a duplex stick built house.- Original RV park was started in 2008.

Water and foundation issues are a big concern in some parts of Sioux Falls.