First take a breather... Worry about boot camp, MCT/SOI, and your MOS training first. You need to serve for a bit before you start applying for MECEP.
The whole idea behind MECEP is that you have proven yourself as a leader (or at least show potential as a leader) and the Marine Corps will now pay you to go to school, get your degree, and become an officer.
MECEP is about a sweet a deal as it gets, and I highly encourage it. I was accepted right at the end of my first enlistment, but I know some guys who got in after about 2 years. Having some college under your belt will make you look better to the selection board, but I went in with nothing. You are basically "stationed" at a college and get paid your full salary to get your degree. You go to OCS your first summer and get your comission upon graduation from college.
My advice: keep it in the back of your head and about halfway through your first duty station in the fleet, start putting in applications. Be smart during your enlistment, and excell in everything you do. You should do this regardless of your plans, but the better your jacket looks, the better chance you have being selected. Enjoy your time as an enlisted Marine. You will learn a lot and have the time of your life (if you're smart). When the time comes, find an officer (ideally a mustang) who can help you out with your package. I never would have made it without the help of my operations officer. Lastly, do well this last year of school!!! High school grades play a huge part with MECEP, especially when it comes to getting accepted to a school.
Semper Fi