EDEN would like to pay me the previous 4 months' rent but I have to fix issues all the little issues in the house, such as fixing hole on the wall, changing the battery for the smoke detector....). 

In some cases I have cut out the entire subfloor up to the wall edge and laid new subfloor.

It does tend to keep laziness and lack of effort from breaching the wall. 

I went in, fixed drywall, painted walls white, paint cabinets, corrected floor slope and put down hardwood.

If 2 and the bathroom is on the second floor, the plumber will need to access the other plumbing/water lines and this could involve accessing walls and ceilings in various areas depending on your layout.

Afaik, the code requires only if you have 4 units that are sharing walls.

I'm wondering if it's coming from a floor drain, a sump, or seeping in around the basement walls?

Wainscot covers a lot of lower wall issues.9.

From working on Wall Street to just diving in when working a 9-5 job and educating themselves tirelessly at every given opportunity... 

If it's in decent shape, I would do a couple upgrades to appeal to potential homeowners (adding window shutters or bark mulch outside, an accent wall, nicer light fixture in living room, etc. etc.)