That reminds me that I'd heard someone had bought really "normal" homes, but had themed them and it was really successful. 

I would tell her you are reminding her of the lease terms and the late fee is a cost that is an option if she wants more time to pay.

Just a good reminder that every profession has good and bad.

And my wife keeps reminding me that I was supposed to stop at 10.

It shows the minimum sqft for the number of occupants.For 1-2 occupants: 120 sf living roomFor 3-5 occupants: 120 sf living room, 80 sf dining roomFor 6 or more occupants: 150 sf living room, 100 sf dining roomRegardless of the number of occupants, for bedrooms the rules are the same 50 sf/occupant and a min of 70 sf for one occupant.If you have that many people coming and going, you need to remind the tenants that only those listed on the lease (and their children under 18) are allowed to live there. 

I reminded him that I told him it was a bad idea, but he wanted to do it anyways. 

Also, just a reminder that you are financing 96.5% of the purchase price, so it's going to be very very hard and almost impossible to have "Actual cash flow" (this is when you calculate in vacancy, cap ex, maintenance/reapirs) in your numbers.  

Tell them if they're unhappy with living there they're more than welcome to move out.If they complain a second time, remind them they're more than welcome to move out.

.: yours is a really good reminder), but does anybody also have any experience doing this "mini-mortgage" scheme that Avery Carl depicts as relatively common? 

For future situations,  reply to their 30 day notice with a confirmation letter listing your expectations for deposit refund: clean appliances, trash removal, yard maintenance, etc. and remind them of the 30 day stipulation so there is less chance for dispute.