Walls, painted white and cabinets sanitized or painted to remove stains and residue, New light bulbs with natural color, not the LED type, Fix floor tiles if necessary.

This is certainly one of the quickest way to get the residual income snowball rolling.

I understand that real estate creates reliable residual income with renting, and flipping fixer upper properties can make you good money as well.  

The easiest way to do it is to find the residual land value and then discount it by guessing how successful you might be.Do that for several product types and you'll see which is the most profitable.

Sometimes you can use the needle-nose pliers to grab the top end of the hairball, if it is visible, and pull it up.You will probably come up with a wad of hair with soap/shampoo residue on it; it looks like you're gutting an alien from a sci-fi movie. 

As far as moisture, I look on the wood for white residue as a sign for concern but I don't see anything like that in your pics.

I would love to own property and have residual income to live comfortably and happily.

Construction adhesive glues it to the wall, but I'd still fur out those studs and screw it in so I could have it as an access panel.The only reason I thought about this is that I just got a new Kohler Choreograph shower surround.You should be able to find leftover composite shower surround material at your nearest recycled-materials supply place.

My Super has expressed commented on their clutter of dishes in sink and days old food left on the stove and  sticky residue on radiator covers ( believed to be jam).

Looks fairly run of the mill water issue...Generally speaking; You have tile, grout, durock board, and adhesive.