As far as taxes, the answer depends on too many missing pieces, which is why the guesses you received (25% and 15%) are not very helpful.

@Jason Munger there are far too many moving parts and missing pieces of info to give you solid advice.

I read marketing pieces from one recently that were technically accurate, but VERY misleading to those reading one of their many pieces in isolation.  

While some properties may be self-sufficient and have great tenants that don't cause a ruckus and pay rent on time; all you need is one that is time consuming and calls weekly/monthly for random reasons, and I assure you, there will be someone who would hire you to take those calls and duties off their hands.There are always going to be those who prefer to keep a hands-on/DIY approach, and there is nothing wrong with that; however, you going after their business will take some time, when you could be using your efforts/energy in finding those who would happily pay for your services; especially if you set yourself apart from the masses and deliver top-notch service.

We looked into grading some common area, prepping it, and installing a smallish piece of playground equipment.  

Biggest piece of advice, make sure the HML you choose is a DIRECT LENDER, this makes a big difference in the investment world.

BTW I will be renovating three of the units kitchens and floors, and refreshing the other surfaces, so these will be a notch or two above the market for my price point.  

The seller and agent could sign a piece of paper hiring an one as a listing agent for 4 hour.

You've gotten some excellent input from @Alexander Felice and @Rogers Smith from the business valuation piece, but in reality, you may not really have a business.  

He installed his own laminate wood flooring very poorly - there were missing pieces and large gaps.