I own a single family with four girls renting it out.

If you are ever going to borrow money later it will likely be at worse terms than the three loans you outlined above.I would invest any money you were planning on using to pay these debts downs on opportunities that pay greater than 5.49% returns.

But my tax returns don't show much of a profit on my first year.  

If your returns are just outpacing inflation in this market because you're risk averse then flipping will not likely be for you.

If you are not looking to scale or you're worried about property management you can invest with a company like Rockwell Debt-free Properties that will return you 8%. 

In return for providing all of the "come up money", the partner would receive 25% ownership stake and, as I mentioned, be paid back with interest. 

The maximum return you can achieve through equity is 3.25% and 3.87% respectively.

@Dan StewartThe founder of Vanguard, John Bogle wrote a pretty good book called "The Little Book of Common Sense Investing: The Only Way to Gurantee Your Fair Share of Stock Market Returns"

Whatever that number is, ask for it in the form of non-refundable additional earnest money on the property in return for extending the contract.

However, partnerships, S-corps, and C corps require an additional tax filing, plus there are wage considerations that go along with the S-corp and C-corp designation, all of which you might not feel is worth the effort of managing.My advice is to schedule time with a tax pro who (a) has expertise in business returns (not all of them do), and (b) does tax planning (not all of them do) and have them help you map out some scenarios to decide what structure will best fit your goals and strategy.