To the OP, you want to join the Navy and you want to know what jobs are good and what aren't well that's all based on someones perspective really.
Honestly MrMeph gave you the soundest advice possible
FINISH SCHOOL but undoubtedly you're going to do what you're going to do and no one will be able to tell you otherwise thats the nature of life.
CT is a broad stroke of the pen there's techs, operators, collectors, linguists and the latest and greatest network specialist. As for IT's while the rating looks good on paper but in reality leaves a lot to be desired.
In regards to how the reserves get treated in the USN, there's this wonderful program (insert sarcasm here) called Individual Augmentee commonly called IA where-in the USN (send the sailors to the army to fill in a spot where a soldier is needed. I could go on & on about the politics of this one but in my humble and thoroughly uneducated opinion this program looks to me like an attempt to justify spending money on a Navy during a large scale land-war kind of a "Hey look were helping see, don't cut out budget" so yeah we fill those jobs (they last 6-18 months) with a mix of active duty & reserve so you've always got a shot at that if you're unlucky.
Mustangs, well we've pretty much got LDO's, CWO's, STA-21's and prior enlisted. I'm not going to nuke this out but as it's been said the text book definition is anyone who has been prior enlisted and becomes and officer is a mustang. The title Mustang is normally one of respect and while it's true some Junior officer may have been in the navy for all of 8months and while in A school converted to the officer ranks it will undoubtedly get them nothing but clowned for claiming to actually be a Mustang.
The important thing is to pick a rate you're going to enjoy doing because you're going to be commited to whatever you take so why not share with us what you like to do? That way maybe some of the experienced folks can give you more tailored feedback vice derail this thread talking about the finer nuances of the military.
..so uh yeah I typed more than I planned
guess it's good to be back on zilvia