I’m worried that if I don’t find a tenant soon, he might pay his next month’s rent that’s due; and then, after I return his deposit, he’ll decide not to pay any more rent.

Your strategy was (is) to make no payments on the mortgage and live there with no monthly mortgage, tax or rent expense until a lien holder foreclosed, which you believe you’re protected against because the borrower on the existing note is in active military service?  

Given your situation, I think the best thing to do is 1) work on improving your credit and 2) look to house hack, preferably a duplex or fourplex where you live one unit and rent out the others.

I don't think you get more rent in 99% of the cases and certainly not enough to pay for it.Also think about your exit strategy.   

Depending on how well the property is run and the rents. 

The rent amount.

"Take rent the day the other tenant leaves but get it paid in advance". 

This one was rent ready but I did purchase under market value to capture some instant equity What was the outcome?

If they rented sight unseen, there should have been an as-is clause in the lease because of that.It does seem excessive given the handyman found nothing at move out (and assuming he did a good job of the inspection). 

Do remember when you rented though and called such companies and could not get answers back on places?