My question is does the past owner owe me anything or do I just have to go to the arm table myself and calculate interest I have paid? 

As the buyer, you would not have to pay that 3% unless explicitly the seller explicitly states they will not pay a buyer's agent, which can be the case in a FSBO.Every state has their own version of the residential purchase contract, but as was alluded to by @Nathan G., you can use a self-drafted document as a contract.

Offer contingency rests heavily on condition of the park and the interiors of the abandoned homes...and assessing whether these homes can be repaired—and if so, will it cost me an arm and a leg to repair 1 or 5 or 10 of them.Obviously, this is a distressed, non-performing MHP, which has a ton of risk. 

HVAC is one of many explicitly defined building systems. 

Make sure it explicitly explains the process for termination if you are unhappy with their services, but especially if they violate the terms of your agreement.3.

Any examples, suggestions, help or criticisms are welcomed with open arms.

One last question that pertains is how a HELOC is figured into the DTI formula... for qualifying purposes, do lenders use the maximum payment and interest rate (ARM) that would be possible on the loan to qualify a borrower?

Driving properties with distressed/add value opportunities and finding then reaching out to the sellers.Another way comes down to reaching out to as many Brokers in your area as you can and explicitly telling them the criteria you are looking for.

Make sure it explicitly explains the process for termination if you are unhappy with their services, but especially if they violate the terms of your agreement.3.

I can only find hard money lenders that are willing to go more than 50% LTV and I'm not willing to pay the 3 points and 8.5% ARM rates that I'm being offered.