Or are we talking digging out a trench around the perimeter of the property to spray foam and dig French drains?

If you discover multiple layers of plaster and/or no insulation I would budget a reserve to gut each apartment back to the studs as they turn over and insulate {We've found spray foam to work best in the older houses, especially if they have rough-cut framing and sheeting}.I am partway though this process with one of my buildings that is 120yrs old ... only I am stripping all walls back to the studs and dropping the ceilings as well.

Can I just spray foam the cracks in the ground with an epoxy or foam?

The best solution is to make sure the garbage is in can and secure where no rodents can get in ad try cleaning trash bin with bleach and spray with ammonia I heard that keeps rodents away.

Since we were not doing any site work, we installed the pump and tank system, along with a fire alarm system.We also needed to get spray foam insulation installed in various areas and with the extra demo, we now had to board and plaster even more of the space, as well as replace the blown-in insulation that was lost.The final delays towards the end of the project were mostly related to some quality issues from the prior three carpenters and plasterer, so add another few weeks there!

I would most definitely spray foam the basement walls. 

The termite company said there was moisture (they did the moisture reading after they sprayed a whole can of foam, not sure if it matters) in the wall so it wasn't covered because there was no visible trace of termites on the soil outside (there is a brick privacy wall that butts up to the house). 

I couldn't see any way moisture was gathering at those places, so we just wiped the area down with a bleach cleaning spray (a shoutout for satin finish paint on rental walls!!)

Some of what was found:- glass in front of both crawl spaces (seemingly intentional)- all of the meters were spray painted over- some rooms were inaccessible due to the amount of trash/furniture in the way- registered sex offender on the propertyThankfully, we walked away.

If tenants do that, can the landlord ask for expenses to clean up anything left behind (or from anything similar for example spray-painting something or building furniture)?