Always check an investor for an existing portfolio and financing in place, whether its a cash buyer check their bank statements, equity accounts, 401K etc.

It sounds like it is too late for you, but you could have conducted a separate test with another provider as a check to see if the first test was accurate or not (had the builder pay for it). 

Example - if a renter were to mail us a check, can I just give them the PO box rather than have them send it to the property address only to be forwarded to the PO box (again, only checking to make sure we stay compliant).

Move the money in and out as tenants move in and out.You need two accounts: checking and savings.

Wondering if anybody knows the legality involved with both of these being checked. 

No.Solutions: 1) Stay out of it 2) Camera the laundry room and check the condition of the washing machine after each time you see residents using laundry, charging the prior user for any damages. 3) If you are convinced it is the mechanic and they aren't worth keeping as residents, non-renew them at the end of their lease.

You need to be careful handling the transactions, like not depositing checks in your regular account and then transferring to your Roth.

You might want to go back and check on those notes you bought for example two years ago and rerun your numbers.

Chat, they will be more willing to tell you if it has services that way.If they are still occupied, know that it may be impossible to insure the house until they vacate, so check out insurance options in your area first.Know that sometimes it is a homeowner who was foreclosed on and they may not accept the foreclosure, may be a sad story, etc. 

Have you checked out local real estate listings or connected with a realtor yet?