Those that do, typically will limit it to very small projects.

It discourages new landlords from entering the market and limits the ability of existing landlords to adjust rents to match rising maintenance and operational costs.

Keep in mind the area surround Temple University has a zoning overlay that limits density beyond what the same zoning classifications allow in other areas of Philadelphia.

However, it might limit your buyer pool, as owner-occupants may be less interested in waiting for a lease to end or dealing with current tenants.

It's clear from your post, and the limited information you put in there, that you are out ahead of your skis here.

It works anywhere within Seattle city limits. 

A lot of PM firms keep contracting work in-house and do not allow outside help from owner's because of timelines, relationships, and of course potential liability.

Those that own real estate will want to be active, those who are limited experience and time look at it as an alternative investment and want an expert to manage it just like some hire a financial advisor for their stock portfolio.

Also, consider the potential for appreciation and rental restrictions, as some HOAs have rules that might limit leasing later on.Given your $20k starting point, a condo could work well as your first step into real estate, especially if you focus on one with a manageable HOA fee and potential for appreciation.

I know certain areas where I live are limiting those types of permits, etc.