You may want to refer them to a mortgage loan originator to be Dodd Frank compliant, but if these people have been able to pay $750 in rent and keep current on other bills they will be able to pay a $500 mortgage .

My question is, to be legally compliant, how does the letter need to be worded, what particulars need to be included, and does it have to be sent registered or certified?

As @Natalie Kolodij mentioned there are several types of commercial/passive real estate that has been structured specifically to be compliant with 1031. 

We will definitely be keeping everything compliant with the proper fund structure. 

If you start-off becoming legal and compliant you are less likely to have issues down the road.

Assuming the dog breeds are compliant with my homeowner's policy, I stated >35lbs = $25/mo/dog and <35lbs = $50/mo/dog. 

I thought about having the PM putting language in the lease agreement for the tenant to not let food go down the sink , tenant would be responsible for any kitchen sink clogs going forward, and perhaps require use of a sink strainer but given there was glass found during the 2nd repair, I am not sure how careful or compliant the tenant would be anyway.In addition.. let's say there is a clog in the kitchen sink with no GD, plumber takes care of it,  is there any concern about the impact to piping long term should residual food waste be allowed to accumulate in the pipes? 

Purchase price: $32,000 Cash invested: $32,000 SFR purchased as in 2017 from out of state investor, required no work (City of Cleveland Heights POS compliant), got a good deal on it because it was rented to a long term tenant paying below market rent (tenant is still there, and is still paying below market rent... which is fine by me for now).

Incidentally if a non-qm specialist LO reading this wants to establish a RESPA-compliant working relationship, I'd be open to it.

She had 12k in it and all she had to show for it was a deck (all 8 sides were different sizes), three stairs (none of them code compliant) and some very crooked lumber that had been left out in the rain. 20k later and much demo of new wood we had her gazebo built.