The tenant is happy and I'm enjoying the added cash flow.

This will allow you to realize cash flow through the construction management while not incurring the tax burdens you rightfully want to avoid.

You can save yourself the trouble and get peace of mind by investing in in properties that are turnkey and will cash flow from day one.

Taking into account my monthly mortgages, which total around $2,300, I'm in a solid cash flow position.Now, as I look to the future, I am keen on expanding my real estate portfolio further and streamlining my growth.

We spoke with a realtor who anticipates a sales price between $475K-$499k.We can't decide if we should sell and pocket about $377,000 free of capital gains tax or continue renting with cash flow of about $9,500 annually after expenses. 

One of your primary considerations should be what % return are you looking for (#2) vs. what are the other alternatives for the money

I would sell the property.You are losing $400 without factoring in repairs, capital improvements, vacancy and potential headaches/time spent.You are likely losing about $800 a month.In my opinion, there are houses that offer both cash-flow and appreciation.My target is normally 8% cash on cash and 4% appreciation.

Yeah if you already have a property that would cash flow and your goal is to stack rentals, I would keep it!

(and place it "at risk" I'm assuming )    Assuming the deal is at least  "average"  for a high end , lower cap rate facility, and assuming that cash flow is sufficient to produce excess "cushion" cash flow at the end of every month -   is this too much net worth to tie up into one property?  

I'm still polishing my investment thesis - for now, I'm doing research into investing in B/C+ single family properties (to start) in Detroit metro area to buy and hold as to generate cash flow.