My background is in trading, so I naturally have to think about worst case scenarios and how a "crowded trade" could play out.

Sellers are naturally looking for someone that is easy to work with, and pre qualified with a reputable lender.

Everything's negotiable.I wouldn't bother with cash for keys with someone of this nature and temperament.

I am looking for insight and expertise with the HVAC system, because I am newer to real estate investing.There is currently one natural gas furnace in the basement that pushes air to all three units and floors.  

Do you like green nature or water? 

First, you can't terminate the lease until the natural expiration date or until all parties agree.Other than that, I would just write a simple letter explaining your intent.

When catastrophe hits, they naturally can't keep up.

If I need to do a double close and pay the fees I will, I would just prefer to milk this thing as much as possible, naturally. 

@Jennifer Marshall, There are large slabs of both natural and synthetic stone in high end tile shops.

I do NOT recommend you get the seller to fix any issues unless they are very easy and essentially cosmetic in nature.