My advice is to not settle for breaking even or even a small profit. 

Too small.  

That's why you see all major corporations/franchises sell the real estate to an investor and then NNN lease it back.Many small businesses don't necessarily get that though.So starting off with that, the seller's accountant confirmed it would be a good move for them.

Fully rented.I'd be interested in purchasing if:1) I can owner-occupy both the first and second floor apartments (the footprint is small and I'd like to turn it into a single family space)2) I can make sure the basement apartment is legally habitable.Can I even legally do this?

You also might want to think about incorporating and writing a small business plan to show commercial lenders that you are serious.

With a 20% down requirement, I am looking to buy in the $500k price range, so likely a small multifamily.

Start small and build a property portfolio and don't take on any debt.

Later we found that we don't need to suffer when we see their emails, we give their cease and decease notice for harassment, and said it will go into their file, then they stopped.Tenants who are picky on every small repairs, and called city for inspection, city came in and picked out 20 items for you  to repair, and costed you money for non-sense?

I know commercial real estate takes a lot of money, so I've heard I should start small with single family houses. 

Given that this is my first investment property (outside of my primary residence), I'm looking to start small to get some experience with the process and taking on the role of landlord.