To name a few issues indicated; units have a known history of water management issues related to workmanship detailing, soft/weak spots in the wood laminate flooring, damaged vent caps on the roof, water leakage in all 3 of the units, condensation observed dripping from main water service, with staining.

You will also want to check curing instructions as any dirt or grime that gets on the caulk before it is fully cured will stain and bond to the dirt/grime.  

This can't be housekeeping (unless that's in the lease), but can be holes in the wall, stained carpet, damaged cabinets, etc.

I would certainly prefer cats over dogs. only thing I know about cats is their pee stains and destroys subfloor, cant do anything about it and must be replaced.

Roof, gutters, fence re-staining, screens, etc...

Most tenants don't do a great job taking care of it and you will have to constantly replace it due to things like coffee/food/wine stains, tracking in dirt, pets, etc.

A flooring guy also told me to check out the Triexta material from Mohawk that is supposedly completely stain resistant and comes with a 25-yr warranty claiming that "you'll eventually end up replacing it because it's an outdated color, not because the carpet failed".

Hand cut and stained butcher block countertops.

Everyone's interpretation of clean is different but sanding and refinishing will remove that dirt/stains, level the surface, and seal it making it 2x easier to clean.

If you have some smaller decorative stained glass windows leave them and just ad storms.