This is compounded by the fact that you've never done this before.  

Which with pretty conservative numbers nets me a 7.7% Cash on Cash (with 25% down) - it goes to 11.8%  for the first year when compounded with equity pay down.  

I have a floor which is very uneven - it bows down in the middle.  

This is further compounded by the hot dry Texas heat and the concrete slab will absorb a good deal of the suns energy during the day (110 degrees in July is not unheard of).

Bow out or sign depending on the research1,2,3

As for leveling the floor, why not leave the concrete and level via traditional means - grinding and leveling compound?

Interest caculated daily to an outstanding balance can cause different amounts, if interest is compounded and made a part of principal on a daily basis, your loan may not be in compliance for a residential property.Sounds you didn't get the type of loan you thought, I'd certainly investigate the note, your closing documents and especially the APR.

But if you are investing the profits as you go, the power of compound returns give the edge to the 30 year.

We have the opportunity to reverse 100 years of compounded complexity in the IRS code by enacting a FairTax system in the United States.

This was further compounded by the previous owner who only raised rents every third year or so.The prior owner was very lax at fixing anything so I've had to play a lot of catchup, the home inspection was lax too about a few things in the occupied units when the initial inspection was done.