While this brokerage would start in Ann Arbor, I would want it to expand to all of Southeast Michigan, then statewide, and ultimately nationwide.As flippers/investors, would you be interested in listing with this brokerage?

Start with BiggerPockets Ultimate Beginners Guide (free).

Under the same scenario, a GP with a fixed percent return would probably make the choice to sell and take profits because they would see the 20/80 decision as a bad bet. 

Ultimately making your side of $1,900 per month go down to $1,220 per month… where can you rent for that much right now…. ?

Maybe someone can shed light on agreements such as this.TIA This ultimately comes down to your relationship with the broker.

This will usually lead you directly to low barrier stagnant markets where the cash flow represented in your spreadsheet does not transfer to reality and the most of the equity is "paper equity" because you will never see it materialize yet many look at completing the BRRRR as the ultimate success.I recognize I am using some assumptions but let's assume you have $100k to invest and purchase and renovate a home in MARKET A for $400K but once renovated the home is worth $500K.

Ultimately, it depends on your goals and the opportunities available for investing your wealth. 

I'm curious if you decided what you're going to do and if you and your friends have made any choices if you're going to invest together?

Your desire for control and liquidity are likely the two biggest assessments you need to make first, as this will start to narrow down your choices very quickly.

(at least for the first few properties) I do not need cash flow in the short run but my ultimate goal would be to retire early from my investment properties.