How many units to qualify as a Real Estate Professional?

[Dave Klein]

If you're a designated Real Estate Professional as far as taxes go how many units are you self managing?

I'm self employed and my day business makes a pretty good income. Employees take care of most of the work so I don't have to be here the normal 9-5.
I also have 13 units that I self manage and another 8 that I have a property manager take care of. I'm looking to add more units in 2021. In order to offset my passive real estate losses against my active income from my day job I need to claim that I'm a Real Estate Professional for taxes (750 hours spent on real estate management minimum).

My accountant tells me that this is an area that the IRS audits quite often because they know it's a really sweet deal.
So my question is to those that already designate themselves as a Real Estate Professional, how many units are you self managing?

I'm thinking about maybe adding a 4 plex and and buying a vacation home that I'll AirBnB. The AirBnB should eat up more time than a long term rental.
Thoughts?