Peter,
First off, I really admire your passion and determination to succeed and such an early age. I was in your exact same shoes about 5 years ago when I wanted to get started.
I would start with implementing a FOCUS PLAN on your whole strategy right now:
1. Buy my first rental
2. Surround myself with successful people
3. Find a great investment strategy
4. Implement r/e investment strategy part-time
5. START INVESTING FULL TIME!
1. Buy my first rental
You can choose to go in either direction here but if I were you, I would buy my first rental first. I would try a more passive approach for buying your rental property (I know you can get creative, but at a young age you have time!)
Do get a FULL time job that pays well so you can apply for an FHA @3.5% down, I would buy this only within the area that I am comfortable with and know it like the palm of my hand.
2. Surround myself with successful people
Yes, do this while you work full time, visit forums like biggerpockets, ask for advice. I would then start trying to develop an investment plan. What do you want to do? Wholesaling, buying and holding, lease options, etc. Once you narrow it down to a strategy you want focus on, hang out on those forums till your eyes fall out. Read from old timers who know that strategy, visit their blogs, ask quesitons, etc.
3. Find a great investment strategy
Now you have a full time job that is going to pay for a down payment on your first rental. A great investment strategy that you found that fits to your like (wholesaling, lease options, etc). Then focus on doing a marketing plan. You should start writing letters in your spare time. Setup craigslist ads, find out costs from printing companies.
My goal is still becoming a full time investor so I want to start a rehab/wholesale business again, but this time focus on setting up marketing campaigns to drive motivated sellers to call me; eventually expanding to more marketing campaigns and hiring employees.
4. Implement r/e investment strategy part-time
Once you got all of the above in place and your focusing on the end target which is do to this full time. I would start by doing real estate part time. Find someone in your local area that can help and mentor you. Surprise them by showing them some ads you have lined up in place, scripts that you've develop for talking with motivated sellers, or direct mail markting cost. If they take you under their wings and you've done investing part time and are doing one deal a month.
5. START INVESTING FULL TIME!
Then, I would quit my j-o-b and do investing full time. I know this is probably not the advice you were expecting and will probably start wondering about those "millionaire" gurus during late light infomercials. I can tell you first hand real estate is not a get rich scheme. With a great focus plan, the right mind set (which you already have), and an awesome mentor. You should be on your way to having a successful full time real estate business career.