You need some type of a reliable method for allocation.

So Get your cost/deal figured out for every feasible lead generation method you can think of ( I was just being polite..

As mentioned above, in the "subject to" method, you purchase the property "subject to the mortgage." 

I understand the 70% rule and I know of (have yet to practice) the fixed cost method for calculating MOA.

I have done well over 150 ceilings with that method and it makes it much nicer than wetting and scraping.

Integrate your methods.

To fix it right, you'll want to keep going until you don't find mold anymore.I disagree with Christian's method for fixing it, but that's mainly because I'd be comfortable "doing it right" without a plumber.

Having been in the field of Marketing for over 20 years now, I've always advocated integration of marketing methods.

Accounting methods can smooth some of this out, pro formas are best guess especially for student clientel.

You don't have to learn how to play poker by going to the high stakes table immediately.