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.

Not everywhere was stained but they are saying they replaced the entire apartment's carpet because they can't seam together replacement carpet of a different color.

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

I looking for any personal experinaces you are willing to share with me the good and the bad not wanting to look at this investment through rose colored glasses.

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.)

There are all kinds of stuff behind those wall that could be waiting to uncover themselves.

Another fine example: we have a house that many years ago someone decided to tear out the front wall, put in a second wall further inside the house, so that they could have a full front porch.