The manning numbers are public record and can be found at
http://www.public.navy.mil/bupers-np.../Pages/IT.aspx
Click the option labeled "Community Overview."
The process goes like this:
1. Inquire about joining with recruiter, officer or enlisted.
2. Take ASVAB test. If you graduated from university in a technical field, you should have a pretty easy time with this.
3. Your ASVAB score will be used in conjunction with your MEPS physical to determine your academic and physical qualifications. For example I got a 99 on my ASVAB (highest possible) but the Navy considers me colorblind so I am disqualified from many jobs.
4. After your basic job eligibility is determined, they will begin a security screening process. At this stage no clearance is going to be granted or denied, they just need to look for items that might be concerning like owning property abroad, foreign investments, etc. This will slim down the remaining jobs available to what you can actually sign for.
5. After stages 1-5, you will meet with a detailer (NOT! your recruiter) who will begin the actual process of selecting a rate. I cannot stress enough that your recruiter has absolutely no control over your job. The detailer will tell you what you qualify for, what dates those jobs will ship out on, and if you need some help learning what they do they can explain it to you. Other than that, it is totally up to you at that point if you take one or walk. If you do select a job, you will sign a contract and swear in.
6. You will enter into "DEP" after signing for a job. This is a pseudo state where you are not technically in the Navy, but are expected to uphold the contract you signed. This period can last anywhere from a couple of weeks to several months until you actually leave for boot camp. In my case, it lasted from early February to mid-August of that same year.
At any point in this process you are free to leave, all the way up until you leave for boot camp. If you decide that you do not like any of the jobs then it is absolutely your right, and no one can take that from you. However once you sign your contract at MEPS (when you select your job) you are expected to honor the contract. Once you selected a job, there were budgetary considerations numbering in the tens of thousands of dollars that were made, and if you back out after that it will mess up a lot of stuff for a lot of people. Plus it is just plain dishonorable.
Once your DEP period is over, you will go back to MEPS one last time. You will do another physical, confirm your contract and terms, then swear in again. At that point, once you swear in the second time, you are in the Navy and all the legal consequences good and bad.
Now you say that you are only interested in IT, but there are other jobs that are in the same field such as AECF-FC and CTN. There are any number of reasons you may get disqualified for a position, so be prepared with backup options just in case.