He owns >20 doors in the East Bay (Richmond, San Leandro, Oakland, etc), none with rent control (Sec 8, Costa-Hawkins, a condo in there last I checked, etc).

Zillow is testing "Instant Offers" in the Orlando and Vegas markets, and it is pretty much the same as what Open Door has been doing in Dallas/Phoenix/Vegas/Atlanta/Orlando/Raleigh-Durham for a while now.

With rents topping at  $600-650/month/door ?

I'm new to rentals (have 5 doors so far), and would love to learn how to be more efficient about the whole PM deal.

It might be different in your market but in a lot of places there are just more people moving in the summer, so you would have a larger tenant pool to choose from, compared to the winter when fewer people are moving. 

I dedicate an hour of my week each and every week to discuss real estate strategies/network with new to experienced investors We meet every Wed would love to meet you there. see details below https://www.biggerpockets.com/forums/521/topics/529240-wednesday-coffee-with-investorsMy team also meets once a month for a larger Real estate meetuphttps://www.biggerpockets.com/forums/521/topics/543296-second-tuesday-monthly-networkingWould love to see you at either of these events absolutely free hopefully you will be able to connect with other investors and add value to each others investing goals

The only other access I could do for that room is add a bedroom door they the Foyer which is a common area.

Do or don’t do question..

Do you think it would be wiser to do or not  to do that?

The per-door cash flows are equivalent to other methods, but you can just keep re-using that same chunk of money over and over again, so none of your own money gets "trapped" in the properties.