So my question is, what is your threshold of late rent payments when it comes to lease expirations and subsequent roll over to month-to-months? 

They own the property because the borrower missed mortgage payments and they are trying to salvage loses. 

And since with FHA, you only have to put down 3.5%, after closing costs and down payment, my initial investment was around $5k I think.  

I reccommend STRONGLY Evergreen to anyone looking for a great note or creative financing payment servicing deal !

This translates to a down payment between $8,750-10,000.

Chase is by far and away the best if you can swing the down payment. 5+ units 500k minimum loan amount.

I'd like to know your thoughts and experience on accepting rent payments.

Rentometer is one such website, but there are a lot of them.But to answer your question about the 1% rule, take the value of your investment, in this case the cost of your house and the monthly payments should exceed 1% of that value.

Assume that you sell apartment A for the same price that you purchased it for, plus interest, and tax payments...Was it worth it?

Research the property tax records and find out the address that the city sends it tax due bills to for payment.