Like @Linda Hastings said, many counties wait until "development begins" before an official street address (I.e., what many investors call a "911 address") is issued. 

I had my contractor paint them (inside and out) with a higher quality enamel cabinet paint after proper sanding and other prep.

As far as money and structures goes,  look at strategies using Options, Master leases,and Subject to purchases which can all be used will little cash if done properly.  

After posting a notice to vacate on the door, if the tenant agrees to leave, is there something I should have them sign to officially terminate the lease and legally take back the unit?

It is especially important in multifamily so you can properly underwrite the property.

I am totally willing to look outside Portland proper, and might actually prefer something outside the city because it seems the regulations are a little more lenient outside of Multnomah county.

Whatever your choice, cleaning, maintaining, and storing your sprayer properly will save you a ton of headache in the long run.  

I want to explore and learn as much as I can before I officially jump in.

I will PM you, I have a few questions on how to properly execute this.

Rather, they move forward with securing additional assets with the intention to make sure they’re positioned properly in case a crash does come.