I installed a/c in both units, painted, and replaced fixtures (light switches, electical outlets with nice white ones, doorknobs with nice steel ones).  

It's supposed to last something like 75 years if it's installed correctly.

Water in the basement could mean you will have to install an interior perimeter French drain with sump pump; I have priced those in the past at $65 to $85 per linear foot of perimeter wall.

Installing cabinets is not hard.New corian or cheap granite counters about $1800.

4) Is $5K a good price from a reputable (probably unlicensed) contractor to knock down one 3 foot wall, two 9 foot walls, reframe, and install tile in the new half bath?

Failure to pay any installment of rent, or additional fee when due is a default under this Lease.If not paid within five (5) days after written notice by Landlord of non-payment and of intention to terminate this Lease, the Landlord may terminate this Lease, and unpaid rent for the entire remaining Lease Term shall become immediately due and payable.

Presuming they were renovated, were they Formica counters and vinyl floors or high end tile, granite and hardwood floors?

If there's water, I would make sure you have a sump pump installed.

I can build an addition for about 120k that contains two "units" of 2bd/2.5ba each with lots of premium features (9.5' ceilings, acid-stained colorful concrete floors, radiant heating throughout, central air, LED lights, granite countertops, subway tile backsplash, carrara marble porcelain look-alike bathrooms, etc.)

For those in Tampa, Fl, what are you paying to have 2 ton AC American Standard units installed?