After one summer of STRs I came back in the winter took a first lean mortgage on the property to replace the roof (and build my RV which I plan on living in while renting in the summer).

Lastly, is it possible to put a “seal” on a current shingled roof, should there be any leaks?

To make things even more complicated, I could possibly have roof issues, which means more $$ spent that I won't earn.

This is not only to make sure that people are taking care of the property, but this is also to make sure that tenants aren't overlooking issues that could be addressed now that cost way more later.These can be minor roof leaks, gutter leaks, mostly to do with water penetration.

The roof was replaced this year and the Central Heat and Air unit was replaced within the last 3 years. 

You just need to shop around more and take care of the big items, like the roof, if needed.

-You'd also want to understand what kind of capex issues you are inheriting....does the roof need done?

Well - sale prices are through the roof right now.

You kill two birds with one stone by giving yourself a roof over your head and an investment property at the same time. 

You should also set aside money as a reserve for vacancies, turnover costs, bad renters, or capital expenditures (roof, flooring, and other big expenses).