You mentioned waiting to save up all the cask to do it all yourself and that sounds doable to you but the seller may not be willing to wait for you.

I moved in March 2017 and have updated all the flooring, all the windows, painted, replaced trim, adding gutters, rehabbed the guest bathroom and there’s more to come over time. 

My goal is to supplement my income and ultimately to replace it.

You probably shouldn't be ripping off shingles to replace roof decking as your first DIY job. 

If your priorities are to invest for income to replace a 9 to 5 personal home ownership should be way down your list of priorities.

Check when the roof was replaced and the age of the mechanicals too.Good Luck!

We did our upgrades incrementally,  with emphasis on the common area upgrades/landscaping plus repairing/replacing broken appliances. 

We have a few furnaces to replace and AC's to install (possibly- see below).2) What does everyone estimate the value of central air to be in a upper-medium-end rental in Minneapolis?

I’m just guessing that if you’re in a $90k price range or less then you should absolutely go for a 3rd property, just get the other 2 rented and get yourself comfortable but sounds to me like a marvelous opportunity to rapidly scale your investments!!!

It sounds like it is above the price point you are targeting, but it may give you some ideas based on the house-hacking method we used as an alternative to buying a multi-family!