I am strongly considering opening a Self Administered, Self Directed i401k so that one of the investment vehicles can be - you guessed it - real estate notes and mortgages.With that said, I don't want to preclude myself from having a brokerage account to hold cash and hopefully earn some money in the stock market when I don't have the money lent in real estate.My question is this:  Do the brokerages (IE: Fidelity, etc), understand this arrangement?  

I would suggest your decision to join a REIA is similar to buying a new vehicle.

Any vehicle payment you use aside from our normal operations?

I personal have 50-60k in debt from 3 vehicle loans, student loans, credit cards.

What is your first thought about the vehicle your contractor drives?

Non-retirement accounts that are investment vehicles (stocks, mutual funds, etc) will count at 70% of face value. 

There's nobody to tell us what trees to cut, what colors are acceptable to paint the home, when to mow our lawn, what kind of vehicles can be parked in the driveway, where to place our garden hose and trash can, etc.

I'm 19 and about to buy my first 2-4 unit apartment but haven't yet, however if I could of went back a few years with everything I've learned now just make sure you're always learning, reading, etc, don't spend your money on stupid things like cars and clothes, if you get a job and keep saving you should have money for a 5% down payment on a property by 18 or so, if you're going to college you can buy a 2-4 unit (duplex-4 plex) or a cheap house and rent out the other rooms, that can go in general too not just with college, and don't buy a brand new car, get at least 3 years old because a car loses 40 percent of its value over those years, you can get a very low mileage older car if you hunt for it, new cars are financial suicide to young people, ideally don't spend more than 10% of your income a vehicle per year, that may be hard depending on what you do, and invest every penny you can while maintaining a safety net (at least a couple thousand dollars to cover expenses, etc) that way you don't have to pay abhorrent credit card interest rates.etc

Do you know any other investment vehicle that allows you to completely eliminate taxes on gains? 

Since this concerns your retirement, I personally would not 1031 exchange into an investment vehicle that you do not fully control yourself.