Low maintenance building, top-end rents for the area due to the extensive work that was done and the location.

We don't have much capital to work with outside the equity in our current home, but should be able to come up with first/last/deposit on a rental without selling.  

You’ve developed a moderately fast wealth accumulation strategy that’s relatively low risk, enabling you to ride out down cycles, negative cash flows, unexpected necessary expenditures, etc.  

., not a huge monthly cashflowing asset currently.

If it's currently an STR they should be able to provide you with the p/l statement from prior years so you can see gross rents, operating expenses, average daily rates and occupancy levels.

I don't see it as an issue but many still do, at least in my small town where the majority of renters are elderly people looking for low maintenance housing options.

It could cause a low spot where things slow down and then it all compounds until there is a clog.

There are also several funds out there that provide high single digit yields that are low risk. 

The mold house would only be a good investment if you can buy it at a low enough price to cover the necessary renovations.

Quote from @Jaycee Greene: Assuming you pay asking price, I'd estimate the down payment for something like that using a hard money loan (HML) would be around 40% of the purchase price and your monthly payment would be $2,600 with an interest rate in the low 7% range (probably need a 700+ credit score to get that).