It will still cash flow at about $200/door/month if anywhere near full occupancy.  

$500,000 after taxes is likely close to $325,000(maybe more or maybe less).Assuming cash-flow from rentals is offset by depreciation, you would need $325,000 of annual cash-flow from the rentals.If you can get $200 / door / monthYou would need 135 doorsYou can work on this type of math to figure out how much rentals you need.Be mindful that rentals require some type of work.

Say there’s a way to sidestep the door-opener issue.

Did you check a next door comp that just went into contract?

I have contractors and home warranty for each of the 8 doors.  

Best way is door knock, cold call and do the dirty work to find those sellers needing to sell.

It's a great way to get your foot in the door in your local market and offset your mortgage while building equity. 

.- Most cities do NOT care if an owner lives in basement, but will not allow a tenant to unless baement has legal egress window.3) Check local statutes if any limitations on how many unrelated roommates are allowed.4) Check with local building dept to see if rental inspections and corresponding requirements.5) Local statutes allow locks on bedroom doors?

What do other property managers consider, actually do, or add to their tenant screening criteria to cover retirees?

Not going to be anything crazy but will get you in the door.