I would think it would increase the sale price as well as ease of bank financing down the line if your owner financing buyer wanted to switch to a bank loan and cash you out.Any idea on the cost these days to pour footings and run a cinder black perimeter wall for an already placed home?

After the inspection, I paid a company to install a basement drainage system that involved trenching out around the perimeter and installing drainage and a sump system. 

you should seal the house. it is not expensive.walk the perimeter. fill any holes you see along the foundation with mortar, spray foam, steel wool, etc.then go in the basement and do the same along your rim joists and any other holes you findyou have to be thorough. mice only need a dime sized hole to fit thru

I am a little confused about the expansion gap required around the perimeter of the room.All the rooms I'm installing in have a baseboard only. 

Then rest of lot graded so Zero puddles even after a fast 2 “ rain.Then downspouts getting ALL Exhaust water at least 5 feet.If you still have any moisture inside you may need interior drain tile and a sump pump around complete perimeter wallsTHEN think of Rebuilding walls in correct way with moisture barrier and air space.

Most Atlantans at least divide the city as ITP and OTP -- inside and outside the perimeter. 

That led to taking down all the drywall and discovering that the french drain they  “put around the entire perimeter” only goes 3/4 the way around.  

I do suggest regrading too but you should only have to do a few feet from house around the perimeter, not the entire yard like what @Joe Splitrock is saying.

Just started a new flip and the basement is a mess, it’s currently partiality finished with wood paneling on about 1/2 the perimeter walls that are just attached to wood strips glued to the walls.

Any advice on how  a single mom can begin househacking in a HCOL or on the perimeter?