I'm going to be completely honest with you, but don't let this demotivate you. Your experience could end up being very different from mine.
1) I'm a Tomahawk FC. Our equipment is old and outdated, but rarely breaks, and is rarely actually used in the real world, so we don't do much. On a ship, "doesn't do much" = gets loaded with shit work because you're a resource and they know you have the time to do it.
For other systems, your mileage may vary. I'd still recommend thawk, however, as a lot of them just do their job and get off at 1400 everyday, it depends on the ship.
2) The shit work in question is sweeping, painting, drilling, etc. On my ship, there is a huge rush to get the big, shipwide things done, and lots of horrible planning. They will tell us to paint a passageway that takes 4 days in 2 days, and then ask us after the first day why it isn't done yet. Because we rushed the project, we inevitably end up going back and doing it all over again a few months later, and again, and again.
Once again, you are a resource, and you will be required to do others' work when yours is done, or work later than you have to to make someone look good. When/ if your system fails, it is your responsibility to fix it. You won't get help from other divisions because of how easy your job normally is, and you will work very late days/ nights until it is fixed.
3) Priorities. When you are in school the navy's priority is to train you and send you off to the fleet. When you are on a ship, your priorities are whatever the chain of command decides is important at that minute. You may be working with your system, doing your primary job, when you hear a call on the 1mc to muster on the quarterdeck to sweep water. No forewarning, no plan, just drop everything and do what they want. It may be incredibly pointless or stupid, you may have much better or more important things to do, but that doesn't matter anymore. You are a resource.
Now this may sound bitter, because it is. I happened to be a very motivated, and perhaps dissilusioned sailor. Ever since the first day I stepped onboard it has been nothing but a slew of dissapointment.
The money is good right now, and it, along with the various certs and quals I get will set me up for the future. However, I would not recommend it to any sane human being, and I hope that your experience is better than mine.
If you have any further questions, let me know. It may take some time, but I'll get back to you.