As far as a tenant installing an air conditioner, I'm not worried about that too much as it's not a complicated process.

For cooling, we rely on seven window unit air conditioners and free-standing window units. 

Add a few window air conditioners you don’t have enough power.  

Me: "Do you mean your air conditioner isn't working?" 

We have one of these heat pump water heaters, it is like an air conditioner in the space you put it in and ours is a tank heater.

Shampoo and Conditioner seem to be pretty common.

If your hoping for repeat guests (where they pay full rate and you don’t have to share it with Airbnb or VRBO), then provide hotel size shampoo, conditioner, body wash, small toothbrush and small tube of tooth paste.  

They did "2 things you should never be without..." and when the person visited the website it talked about you should never be without an Air Conditioner...

(short tangent below)I recently had a house that had a window air conditioner in the wall to cool the dining room. 

In that case I would purchase four window style air conditioner/heaters to mount into two of the windows per unit.That means each apartment will have two units they can control and this will be more than enough to heat and cool 1000 sf or less providing you purchase them to accomadate the correct square footage.The pros and cons of going this route:Pros:Cost.