I realize we’d probably want to bring in a real estate attorney, but I’m assuming there are models in place that are probably well-established for such a partnership that I know nothing about.

For example I am near old town alexandria and the businesses are 200 year old row homes and there is no place to put ramps to get in establishments and door openings are not wide enough, but that is because they also could never comply. 

When it's a well established company like Apple, they aren't likely to be going out of business so there is some certainty that there will be in increase in demand for quite some time.

If the tenant fails to establish their own policy, enroll them in your renter's insurance policy and charge it back to them.

I'm aware that I'll have to talk with a zoning board to rezone a single family lot to a multifamily lot.

Yes, there’s still a lot to learn and accomplish.

Its good that you've already established some target markets, I'd recommend diving deep into 1 or 2 markets, then branching out. 

It's not a get rich quick scheme, it's a lot of active work and I would have 5 yrs in my head at a minimum before you truly become established and stabilized. 

Small talk, showing empathy, and expressing genuine interest in their situation can go a long way in establishing trust and goodwill.Be Willing to Walk AwayOne of the most powerful negotiating tools is the ability to walk away.

So that has a lot to do with it.