We try to get ahead of the issue by preventing it in the first place.

@Kyler Tarr it's good you haven't had an issue but you also mentioned your property has some knob & tube.  

The main issue I have is contemplating the baloon payment at the end of the 2nd year and refinancing the remainder with a bank...how can I compute that into calculating the IRR?

Issues 1) even garage conversion ADUs in single family zoned areas typically cost more to build than the value that they add.  

Would ownership by a SC entity resolve this issue?

We currently use Hospitable for 12 properties, and it's working fine, no major issues, and I know they've been expanding with new features.

Also, keep in mind that if you do self manage, you do put yourself at more risk for a legal issues.

This also begins YOUR title seasoning, so that when you're ready to take out a traditional mortgage, you can refinance and pay off the seller without a title seasoning issue. you can buy title insurance from the title company at closing. this is a good idea. 

First time using a contractor to fix a few issues at my property before putting it in the market.

If it is a private money/ commercial style  lender, it is a relatively simple process.