Both Guesty and Track let you set this up easily.  

Although I believe I can see the path to my first rental easily, I'm having a hard time figuring out how I'd get to the next one. 

There are so many lost opportunities relying on assumptions that aren't accurate and easily verified.

We self-managed 20 properties while working 2 full time corporate jobs pretty easily.  

You should be able to do that fairly easily.

In a place like SE Michigan, we are lucky in that prices are low enough that you can find deals in solid neighborhoods that easily return well.

I would also say that markets like Manhattan are not super representative of most markets in the US - a lot of foreign investment I'd imagine in NYC, Miami etc - I'd guess a lot of these cash purchases are more about exchanging unstable or risky foreign assets/currencies for perceived stability/safety of US top metro residential real estateI think in a lot of other markets where this isn't relevant - I think most are cash offers being "king" as not having appraisal or other contingencies that might sabotage the sale after 30 days or so and make people re-list (sellers will take less to avoid this risk and downside)

Once you’ve got the hang of that you can easily repeat the process or go bigger.

If it’s a smaller home that has a high occupancy already it may not be worth it, small homes (1-2 beds) that are priced and marketed well in the Denver metro can easily stay over 80% year round.

I also think you could easily find what you're looking for in the Gold Coast - which is a little less hectic than River North and gives you that Lincoln Park vibe as well.