Would it be better to purchase multi family property or  (1 - 4 units) .... single family property or does it matter ?

The banks typically want to see some track record before letting you GC your own builds, especially since it is not your primary house (I know my bank does)Most builders only doing a few houses will be at a % agreement, and if you do get them to agree to a flat fee, they will likely just figure out the % of the build, and give you that number.Something to consider, if you dont have experience on builds, cost plus could really get you.  

All the buildings in this neighborhood are multi families and owned by investors.

As a former accountant, I love crunching the numbers on multi-unit investment opportunities.David

I don't invest as much as you in debt, I prefer equity but your track record in PoL is excellent.  

Also, create an execl spreed sheet and update monthly to tract expenses, income, mileage etc....You could also look in BP file place to find someone else's tracking sheets.

Professionals with decades of experience and very impressive track records do all the heavy lifting for you.

The other thing is that most of the multi units are in not so nice areas.

Does anyone have suggestions on a utility for keeping track of my campaigns and documenting their success?

Someone to track down dig leads within a defined district or zip code.