Other structure suggestions welcome too, but an answer to the interest rate / return question would be really valuable. 

I have already gained so much knowledge from the BP community and I have only scratched the surface. 

Depending on the sweat equity I gain I may sell the house or use it as my first rental property.

One valuable lesson I've learned through out my negotiations so far is that I can expect anyone/everyone involved to attempt some variation of this, but that it's not productive to get angry at them for it. 

I would recommend, depending on your level of experience, attending a few Real Estate Meetups in your area and sticking your head in the forums for a while to gain as much knowledge as possible before you pull the trigger on anything. 

That doesn't change the fact that the vendor provided a valuable service... only who would pay (or contribute to) the bill.

What are you doing to gain such success this early and if you were to double down on those efforts now, how many units can potential grab by year end?

So here is the question: Would I have to pay capital gains on this money I receive since it technically isn't "profit"; it was money I SPENT and am merely just getting back.

ORDo you think it is better to sell and invest that money in something that would gain interest or profits over the next 7 years?

Realizing that is only one opinion and encourage me to prove him wrong, I want to gain additional insight for guys who have experience in self-storage.