I now own 9-units here in Columbus and have BRRRR’ed and Flipped multiple properties after.  

I have units where we provide washers and dryers.

A decade ago it was all about buying a fourplex with 3.5% down, and the rents from just 2 other units would cover the entire mortgage.

It is 2 unit building that has potential for a 3rd unit as well. 

It's particularly helpful to inquire about the promptness of rent payments and the condition in which the rental unit was left upon vacating. 

With your seed money, starting with multiple units right off the bat could leverage your entry into real estate investment and rapidly scale your portfolio to help you replace your 9-5.

I am trying to understand if they would be any challenges with purchasing a lot that has quite a few oak trees as they can't be removed as there are policies around tree removals. could i build a small office commercial unit of about 5000 sq.ft in this lot?

We're located in Berkeley, CA, and own a parcel that has a 1000sqft house (2bed/1bath) in the front and a 2x800sqft unit (1bed/1bath each) building in the back.

I would evaluate the issue in the same way I would if the unit was vacant.

That would unite all interests.