It has its own court yard that could be used as a glass-covered atrium with a common area for people to relax.

You make your money when you buy, so you want to buy low enough to have enough margin to cover rehab plus your profit at the end.

I know how buying a house for a primary residence can become an emotional decision which increases the amount a person is willing to pay... but with attempting to pick up a long-term buy and hold, at least in my experience, the profitably is largely determined at purchase (and of course subsequent to this, proper tenant screening and management of the property).

Then 10 years into it, my cash flow was up to $30K/year, including covering several thousand a year in small nuisance repairs.

It's all a game of creating barriers of exposure to your other assets and if you have a big enough accident at your property, insurance will not cover it most likely. 

Plus, you'll want to create an upfront operating account of 1% to 5% of the purchase price to cover unexpected expenses before you've accumulated enough money for the $250 to $300 savings.For SFRs or smaller multifamily, as you said, it depends.

@Gab Loo @Hannah Peerbolt wrote a good blog that covers a lot about what to look for in your property manager.

My goal is to do a full 20, get out at 42 years old, and be done working with enough money to cover expenses + have ~$10K/month excess.

Screening - run credit - background checks?

As you found, a rejected application because of your bad referral means you are stuck with the tenant.Eventually though they will only be able to rent to folks who don't screen, and those are usually the worst places who don't care about bullet holes and pests and rodents and code violations.Don't ever stop your eviction process until they are out of the property and you have keys in hand and have assessed all the damages.