We are life long El Pasoans and currently live in Horizon City. 

Up until now my partner and I just split the profits 50/50.But now with 2 other potential investors on the horizon how do I make it fair for everybody?

(make money like a new home builder)There is also the subject of BRRRRing with the local banks (or 21st Mortgage or private money) and what they would rather loan against.From a purely business point with a 15-year cash out horizon on a portfolio of 20 or so homes (or maybe a longer horizon with 50+ homes if I decide not to conquer the world and just do this until I die) which would you all do?

And in many cases he's almost a 50-50 partner with you.Contrast that with the longer term horizon of rental investing. 

Only a portion is PMI.Personally I think the answer about your time horizon is the best: if you wont be selling in 5 years, then it's safe to put less down.

Do you think it is possible to invest /develop/ compound this portfolio to the top i.e hundreds of millions/dare i say billion - I am 30 years old so have a considerable time horizon to compound returns ahead of me2.

Do you think it is possible to invest /develop/ compound this portfolio to the top i.e hundreds of millions/dare i say billion - I am 30 years old so have a considerable time horizon to compound returns ahead of me2.

I am looking at a property that looks good and the math works, but it's a little more expensive than the last few properties I've looked at, and  although I have enough available for a 20% down payment, I'm hesitant to tie up most of my liquid cash into one deal, especially if the market might be getting soft soon and there might be good opportunities on the horizon.

This was a deal I believed was good and profitable, and as of now have not seen any trouble in the horizon.

Then back out those goals to achieve them within the time horizon you're looking for.