That's accumulation for personal gain and desire. 

Liquidity...and the power of compounding future investments with the 30 year mortgage, that you don't have with the 15.Example:30 year mortgages - 3 years 4 months, CF = $20k accumulated. 

A greedy, selfish person accumulates as much as he can and refuses to share no matter how much or how little he has.The money matters little.

Scrooge was considered financially free, but he loved his money so much, the accumulation of wealth made him not financially free.  

My wife and I are currently finding out that the cash flow coming from our SFR's is plenty as we build our portfolio and the more we accumulate we will then be adding in 4-plexes and then apartments.

Buy a $10 coffee maker at Walmart and make your own coffee.it is extremely important to live below your means.While I would say this as "spend less than you make" this is the absolute key practice to accumulate any wealth. 

Over time I want accumulate a portfolio of 1,000s+ cash flowing multi family units.

If I sold it, can I keep 50% of the gains to pay off some debt accumulated from the renovation and use the other half on a down payment for a larger property?

This is what keeps people stuck in the poverty cycle.Wealth isn't about accumulating things to make you happy.

My goal is to accumulate a rent roll of about $150 annually.