I also have been reading/studying/jumping around What Every Real Estate Investor Needs To Know About Cash Flow.I hope to put a plan in place in the next few months, and then practice running deals until I am in financial position to act on a deal. 

It took us years of researching, studying, taking losses, learning tactics and building relationships with neighbors & police in certain areas.

Long story short, after trying to sell it for 5-years, and spending more than $150K trying to maintain and improve it for sale, we lost the house to foreclosure because i spent all my money trying to maintain it.

Hello, I am an Investor now studying to get my license!

I haven't made a dime that I could reinvest in something other than just maintaining the duplex and the basic cash flow to operate my new little side business.  

Would you say that a rather nice, well maintained 4-plex in a C area would be a B in a C area?

So for an REI there will be a brand new opportunity cost, coming very soon, of maintaining perpetually high mortgage balances.

My advise is to do all three of those things when necessary to maintain a good reputation in the industry.

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

I'm learning the investment side now and have studied a lot!