We called them, they said they were out of town on some sort of family issue, and would send in rent. 

REI was one of them but due to financial issues I had to postpone my dreams of investing in real estate, fast foward to now Im a local CDL truck driver and in a position where I can start planning again for the future to finally become a RE Investor.

I was trying to consider some factors that may come into play - from what I understand you can put as little as ~3.5% down under an FHA loan - will it be more beneficial for me to put "more skin in the game" with the largest possible down payment I can make (say, closer to 10-15%)?

This is definitely more of an estate planning issue than REI.You'll want to discuss with an attorney of your choice.

I only wanted to know a good time to be there, so I don't keep having this issue everytime I go there.

I did something like that just once when one of my tenants had a bank issue. 

Issues that I cleaned up myself long after he was gone. 

I wanna buy properties well under market and rent to own to people who have had credit issues or maybe other issues.

Luckily, they have a great inspection with no findings.Though not optimal, I decided not to pursue my $50 late fee and the whole issue with my renters breaking the lease by using their deposit as the last month's rent.I'm curious if you all know of a more functional approach to this whole last month's rent and  deposit thing. 

Major structural issues with the duplex.