I have limited knowledge in real estate and about 15k saved to invest.

For one, that would be a gift in excess of $14,000, which exceeds the annual gift limit. 

My questions are:How did you structure your business (S Corp, LLC, Limited Partnership)?

I do have a limit of ownership ($ of property owned) before I create a new LLC to help limit the liability somewhat. 

Very powerful method if you do your homework and due diligence on the repairs.

I want to say as early as possible but I think there should be a limit.

I agree, In my case I won't offer if I see there is a serious foundation problem, under or near high tension power lines, too near a cliff, flooded, burned, drug house, war zone, more than 3,000 sq ft, under 1,000 sq ft, clouded title.

Once over that limit, no matter if there is or is not any debt, PenFed will not move forward. 

., The half you lived in will be tax free to the limits of the sec 121 exclusion as everyone has said. 

--A requirement to insure the STR through a limited set of STR-specific insurers... discussed ad nauseum elsewhere on BP.