We have sufficient financial resources and plan to go slow with a conservative purchase when opportunity knocks. 

If kids are playing on it a 12 mil wear layer will be more than sufficient.

Should I develop my own plan with an architect that I could use over and over with minor modifications or is something on a site like house plans.com sufficient?

If the tenant deposits in cash and request for a receipt in my name shouldn't the banks deposit slip be sufficient?  

As long as you've documented the damages sufficiently, there shouldn't be any issue.

When a policy's credit/dividend exceeds its premium payment requirement its said to be self sufficient.

The information you provided on the opportunity is not sufficient for anyone to help.

Also keep in mind, does the town/city have rent control laws that would prevent you from raising the rents sufficiently?

I can definitely answer your question, here's what I did with real examples.1st House Hack - 4 unit - I purchased this multifamily in August 2017 with 7% down (couldn't do 3.5% down because of the FHA self-sufficiency test).   2nd House Hack - 1 unit (single family house with mother-in-law apartment) - I purchased this property in the summer of 2018 with a 5% conventional loan (a little over a year later), and I was able to move out of my unit in the 1st House Hack and into the basement apartment of this house hack.

The only thing you'd need to do is prove self-sufficiency which is the other 3 units will need to throw off rents to cover the mortgage.