Rehab cost is expected to be 90K (this old home eats up the budget very fast).

Looking at your deal my fear would be your initial repair costs becoming more than you the property is worth and eating up your cash flow.

Cap ex, maintenance, management, and vacancy will eat you alive. 

For houses built after 2010 ish in a master planned community, they eat lunch+ dinner and breakfast for next day .

If you are not going to occupy the property, you will be looking at 20-25% percent down payment...which will eat up your cash quickly...and if the property needs repairs, you have no cash to make repairs...reserves are important to think about as well.Your best bet sounds like a house hack in a small MF property if you want to be outside of the ghetto.

If true, this creates a bit of a chicken and egg problem. 

This doesn't necessarily happen with every deal and the stronger the cashflow (and higher the Rent/Value ratio) the less likely it is that the depreciation loss each year will fully "eat" the cashflow, which would put some additionally income on you personally most likely)Those things aside, I still think ConC is the most valuable metric here. 

Also, if an investor is bringing money down, how do you structure the deal to either buy them out as soon as possible or the repayment isn't eating all the cash flow? 

The way I got started was that from the ages of 17-21 I had been saving like 80% of my income and eating like a dog.

Not be a favorite place to be when you're in quarantine and locked down in a 400 sq ft apartment but if not in quarantine and you can walk to Fenway or eat at 5 star restaurants downstairs from your apartment, it's a whole different story.