This assures that they'll gradually get their money back AND make solid returns at the same time.

If you want to keep this plex property long term after you move then I'd suggest keeping the cash flow and let your tenants' rents grow the equity gradually over time instead of dumping extra cash into the house to grow your equity faster.

We started off in really rough stuff & have gradually focused our attention on higher end properties as the war chest grew.

If a property with those parameters should produce 6-8% returns with gradual increases as the market rises.

In contrast, if you gradually make principal payments on your $1 million of pre-TCJA home acquisition debt, you won’t be able to treat any portion of an additional home loan taken in 2018–2025 as home acquisition debt because your existing loan will absorb the entire $750,000 TCJA limit."

As the boundry line of Detroit spreads to other counties, it gradually adapts the same scenario.  

During the first summer of ownership i attempted to raise rent (gradually) $100 to a total of $700/mo.

My plan to get started in REI is to rent my house out, I bought it when the market was at its low and now the market is gradually coming back up.

If you are trying to switch careers, my suggestion is stick to something that you know, and do real estate on the side gradually. 

My experience tells me to not view your situation as standing at the base of a 30,000ft mountain but a gradual hill that you have to cast aside frustration and make the steady hike up.