It's been fine for 4 years and now water has found a new way along the wall.

Landlords should provide necessary appliances (fridge, oven and stovetop, hot water heater).  

For a first investment property though, I’d recommend staying away from foundation and structural issues, or serious water damage.

In WA It also means carbon monoxide and smoke detectors and water heaters are strapped. 

I am in need of replacing all the window because I noticed that water is getting inside the apartments and is messing up the Interior drywall.

Here are just a few examples: missing handrails, no gutters or broken gutters, exposed subfloor, exposed wiring, insufficient heating elements, dry rot, mold, water damage, rotting or leaking window sills and trim, appliances that don't work, deck and fence in disrepair, wet basements, peeling paint, roof over 20 years old could get called out.Hope this helps and best of luck to you!

Landlord’s Duties (KRS § 383.595)Landlords must supply running water and reasonable amounts of hot water at all times and reasonable heat between October 1 and May 1.

There looks to be an old water pipe going through the slab as well.  

Lastly, I would build in some replacement reserves into your figures as roofs, HVAC, water heaters, appliances, etc. all wear out over time and need to be replaced. 

Once the whole thing tanks, I would replace with a unit that doesn't have a water dispenser.