Think about future enhancements that can bring in leads.

You should be able to find some historic data on appreciation rates for the Greenpoint area to support your estimated appreciation on a pro forma basis.As a side note...estimating appreciation is a great exercise, but there is much more to consider on an an asset and project of this type. 

PROFESSIONAL INSPECTIONS AND INSPECTION NOTICES: Buyer may conduct at Buyer’s expense (unless payment for such expense is otherwise required by governmental regulation) any or all of the following inspections of the Real Estate by one or more licensed or certified inspection services: home, radon, environmental, lead-based paint, lead-based paint hazards or wood-destroying insect infestation, or any other inspections desired by Buyer in the exercise of reasonable due diligence.

It is easy to exercise when you are in the habit of exercising.

I enhance the spreadsheet by adding a further calc at the bottom of each month that subtracts expenses from the rent, then also the principal paydown which is automated based off the interest input.

Poor work ethics, drinking on the job, etc.If he does not finish you must exercise whatever stipulations that you have to resolve a breach in contract.Seek legal advice and have an attorney tell you what can be done.Depending on the state there may be a fund that you could receive damages from if he does not finish.I am no expert, but your contract should have been created by a lawyer or at least reviewed and include what you can do and should do in situations such as these.

One of my mentors had me do an exercise about coming to grips with one of my biggest fears, which at the time was fear of embarrassment.

In my case, a steak dinner is a tradition but the major portion of your funds should only be used to build, protect and enhance your asset’s ability to produce and sustain income generation.By taking on responsibility in the housing market at such a young age, you will have some added benefits and opportunities coming to you.

...what would you do with it?

(Obviously, I'm looking for purely RE related answers)

So let's say we agree to pay $600 a month with $100 a month credit towards the purchase.You start you're repairs and complete them in 30 days or less and let's say you purchased $1,500 in materials.Now you place the property on the market because you have the option to purchase "You have taken control of the property with your option".Let's say this deal has taken you 90 days from the beginning to the end.You find your buyer let's say at a great deal of $95,000 - $5,000 below market value at this point you would simply exercise your right to the purchase option and do a simultaneous close.Now let's run the numbersYour option purchase was $80,000Your option credit of $5,300 (Repairs, materials cost, labor & monthly credit)Your purchase price after credits $74,700Your buyer purchase price of $95,000Leaving you a gross profit of $20,300You had out of pocket material cost of $1,500You had 3 payments of $600 each with $100 for the credit purchase with an out of pocket of $1,500Carrying cost of $600, (Real estate taxes $300 &$300 Utilities)Advertising cost $300Closing cost $1,300Your net profit $15,100You simply took control of a $100,000 property for $3,900 (payments, materials, utilities, and advertising) and turned a profit of $15,100 in 90 days!