I've worked with a few CTT's and they are NEC driven. Not more than 6 years ago they merged with the EW (Electronic Warfare) rate. SO depending on what type of training you get after A school will determine what you do. Although their jobs are similar in most respects there are small differences in the details. I believe that your rate is what you make of it. The navy is what you make of it. Some love it and some hate it, others are just along for the ride. If you go in with an open mind and a good attitude, things usually work themselves out and people enjoy their job. It's the few bad apple with negative attitudes and laziness that ruin the job. Ultimately it will be the people you are surrounded by who will make your time in the military good or bad. When you have a good crew to work with, no matter how crappy the job is you still have fun. When you have to work with a bunch of people you don't get a long with, you could have the sweetest job in the world and it would still suck.
My advice. get in and put 100% effort into whatever rating you try. ANd i bet things will work out for you just fine.
As for the difficulty of A school, it shouldn't be hard if you study. The reason you take the ASVAB is to match you academically with a job you can do. So you must already have some aptitude to succeed as a CTT so you'll be fine.