Congrats on your enlistment!
I'll try to give you some info on the ET side of the world...
Once you finish school and get to your first sea command you won't be doing much besides qualifying. On a surface ship you'll start out with a fairly junior watch where you handle the communications for the control room. You'll also take a lot of logs on some equipment that is installed in there, but your main function will be relaying communications from the officer in charge of the plant to the people out in the plant doing stuff.
Once you finish that qualification you'll move on to another watch that has a little more responsibility, and so on until you qualify Reactor Operator (RO) and Shutdown Reactor Operator (SRO)
There isn't a lot of maintenance that a junior person can do. You have to be qualified Reactor Operator in order to test or fix any reactor safety related equipment. You'll be able to watch some of the tasks get performed, and as you progress in your qualifications you will learn more about each system. That way when you qualify RO and can work on stuff you know how what you're doing affects the plant as a whole. That's a really important part of the whole thing, and why it can take a couple of years on a ship before you're qualified RO.
As far as the equipment goes, I really can't go into too much detail. You have instrumentation out there that was designed in the 1950's all the way up to some of the newer stuff that it actually mid to late 90's technology. It takes so long for a new piece of equipment to get certified because we have to make sure that it works no matter what. It's not like you computer at home... If it breaks you take it the shop and they fix it. You ARE the shop when you go out to sea, and the equipment is placed in conditions (high heat and humidity) that it was never designed for.
It just depends on what ship you go to as to what level of technology they have. As you go through the training pipeline you'll hear about which ships and boats have what kind of technology, so you'll have a pretty good idea of where you want to go as you finish school. That doesn't mean that you'll get exactly what you want though, look at some of the other Navy Nuke threads to see that. I can say that in 21 years of service I got every assignment that I asked for... So it is possible to get what you want.
You might end up getting a little more computer time as a non-nuke ET, I really don't know. If real computer stuff is what you want I'd look at the IT rate. There are some other ones too, but their names escape me right now, sorry.
No matter what though I'd highly recommend the Nuke field. It's challenging on a lot of levels, and as an ET you not only get to play with some electronics stuff, you get to learn a lot about the applied engineering field. I enjoyed the job enough that I'm still doing the applied engineering part even after I retired from the Navy! Of course the money helps a lot too.
Good luck, and if you have any other questions feel free to ask... after making sure that they aren't answered elsewhere in the forums first!
Jay