The septic tank seems to be filling up super fast, who is responsible for the bill when it happens to back up into an open hole (which was to be another restroom but was never finished) in our basement/downstairs? 

I finally gotten my house back in order from Harvey in 2017 and have no more money to even put back in my house to finish my restroom. 

Additionally, if I lived in an rv, that would mean I would need to buy an rv—which is a chunk of change in itself if I want a decent one that will provide basic needs (shower, restroom, etc).

So, you need to think about zoning and then other things with which you may need to comply as a business (ADA access, restroom capacity, etc).

I did mention to them that I just want the home to be "rent ready"  (nice kitchen with granite countertops and a very nice restroom vanity) everything else is just base line safe and presentable as you mentioned.  

Plus the reality is that people need to eat and go to the rest room anyways.

At the south end of the property are 15 acres set aside for an elementary school.....Most of the talk (at the recent meeting) centered on the recreation area that will include a soccer/multi-purpose field as well as tennis courts and basketball courts, rest rooms, and parking over a 6.25 acre parcel.....Grand Avian Parkway will have a five-foot wide landscaped median, 5-foot wide sidewalk on the east side and an 11-foot wide bike path/trail on the west side.

The general idea is to renovate the kitchen with new cabinet & counter top; Update all the restrooms; patch up all walls; remove pop-corn ceiling, repaint whole house; re-sand and re-stain all the hardwood floor; some plumbing work; install can lights in all rooms;  move some lighting fixtures; add/move switches and wire for Ethernet.  

I have a house 1,240 sqft, on pier and beam, wooden floors, tile in restrooms (2), carpet in bedrooms (3). 

It was mainly just an upgrade to the kitchen and the restrooms.