By this time I'm thinking one 50-unit building should be able to generate this cash flow. 

There are few ways around this, including a job transfer of more than 50 or 100 miles (I can't remember exactly).You say you want to live in one side, it doesn't sound like you have any sneaky plans, but I wanted to share that it is mortgage fraud, which is a felony, if you say you're going to owner occupy but then don't.

Your total expenses should be around 50% of the gross rent not included debt service.

The broker gets 50% and the property manager gets the rest.

The retail store that I manage I get to talk to about 30-50 people a day during that one week at least 3 are in some sort of house/property situation.

The notes I create and sell are between 50-65% LTV - NOT 150% LTV

So here is the question: if you were looking to build a portfolio of 50-100 SFR, you have 2 great W2 incomes, perfect credit, and $50k to start it with, where do you begin?

Just be careful not to throw the baby out with the bath water and rule out good areas.

Additional info:primary 1031 exchange rules and requirements include: 1) same taxpayer: the taxpayer who sells is the taxpayer who buys, 2) property identification within 45 calendar days post closing of the first property, 3) purchase of the replacement property within 180 calendar days, 4) trading up: the price of the replacement property is equal to or greater than the old or relinquished property, 5) hold time supports the intent to hold for investment, and 6) related party transaction regulations. 

There could be several ways to achieve this but knowing the subdivision rules is key.