So lean on your title company closing escrow as much as you can.In accountant speak the number you subtract from your net sale is the "adjusted cost basis". which is the purchase price plus capitalized improvements then minus depreciation. 

What you will need to know is the number of occupied spaces, the monthly lot rent amount at the park, and the cap rate.First, multiply the number of occupied spaces by the monthly lot rent (lot rent ONLY, so if there are homes rented, only include the lot rent amount for each of those spaces) and then multiply by 12 months to arrive at the gross annual income.Next, subtract the expenses (they can range from 30-50% based on the variables mentioned above, so it's best to use 40% for this quick evaluation).

As long as you know is the number of occupied spaces, the monthly lot rent amount at the park, and the cap rate, you can do this quick valuation.Start by multiplying the number of occupied spaces by the monthly lot rent (lot rent ONLY, so for the park owned homes, only include the lot rent amount for each of those spaces) and then multiply by 12 months to arrive at the gross annual income.From there, subtract the expenses (they can range from 30-50%, so use 40% for this quick evaluation).

When running comps on this house would I also look for recently sold houses in a similar condition to try to figure out a purchase price, or would I estimate the purchase price by look for a recently sold houses that were fixed up and have similar specs and then subtracting the cost of repairs needed?

Should the loan payment for the HELOC be considered an expense and subtracted from cashflow?

So, let me add up all cash payments I received, subtract all cash payments I made, and - voila!

The only thing subtracted from this amount for lending purposes would be the principal payment?

If the end buyer pays for the closing costs, does that get subtracted from the offer price between me and the seller or me and the end buyer?

As for your taxable gain on the flip, here's a back of the envelope calculation:  Take your cost plus all improvements and subtract that from the sales price. 

Take your husband's annual income, subtract the additional income you will make, divide it by the expected proceeds from his life insurance policy and multiply that by 100.