If its a serious thing you want to do as a career I think the MECP is a waste of time at the start. All you do is read a box and take a test. No real hands on experience.
No joke, but there has been people who took this coarse already, apply for a job, and not even know how to do a head unit instal in a simple vehicle.
Some places will even pay for the mecp course after you work for them. Theres a good bit of useful info gained from MECP but unless your actually doing it, it will be hard to do it in real life when the time comes. But then again, I learn things differently then others, and the way I see the MECP stuff is like taking history classes in high scool, hell I only remember Christopher columbus sailed the ocean blue in 1492 because of the jingle that goes with it.. LOL
You are much better taking hands-on type workshops, but they cost a nice chunk of change.
http://www.stevemead...coming-classes/ for example, but this will better yourself better then reading a book.
But again, these corses are something you would want to take after you have a job, and are in a field that you enjoy doing.
The best advice is to find a local shop to you, one that you feel is decent (but being new to the field it maybe hard for you to get the feel of it being a reputable shop or not) but once you find a place, talk to the manager, and try to get some sort of apprentice type deal worked out, where your there a few hours a day, emptying trash, stock shelfs, grabbing parts, and watching the installers do their things.
Just remember in most shops, stereo installs are not the companies bread and butter income. Lots of it is keyless entry/remote start/alarm installs, and there maybe days where you got 8-14 cars to install remote starts on in 1 day, and may not do a system install for a couple weeks!! This is a big misconception to most people and they think they will just be doing a lot of stereo installs.
I don't think it could have been said any better!