However, it does sort out the tire-kickers (if anyone actually kicks tires any more).I'd just tell them upfront the cost and that EVERY applicant (remember fair housing rules) treated the same.

OR, you both own units in one LLC (really, a MMLLC) that owns properties.If the latter, technically the general rule is that the LLC is a partnership for federal income tax purposes and should be filing a 1065 and any related state/local partnership/business returns.As you noted, there is an exception for community property assets.However, treating it as disregarded, when it shouldn't be in this situation, isn't a huge deal at the federal level because of Rev Proc 84-35. 

If the tenant reported right away you may not need to treat other units but I always check all the units because not everyone will report.

This is big- make sure people treat their home (which their room is) as a place that is clean and neat. 

This allows you to treat the property similar to a refinance where you Dad can gift you the down payment and the closing costs. 

Would it make sense to treat the 20% down as a private loan, charge interest to the partnership, and then split everything else 50/50? 

Make sure they treat tenants and owner with respect.

The other part which will lead me to the questions I would ask a prospective STR Manager is related to how a STR Manager will treat my property & guests with the same care as I would? 

My friend is treating me like he owns the entire business since he had the idea for so long, which I get.

He was a friend and treated me like gold.