Jailbreak noob here

Best advice I can give you as someone fairly new to the JB scene: Read. Read everything you can find on the subject. Read it until you understand it, and if you don't understand it, don't try it yourself until you really know what you're getting into. There's a dozen questions posted each week that are from people who jumped in head first without a clue of what they're doing, and now their phone's f'd up. It's all totally avoidable if they'd just read up on the subject FIRST. There's a ton of information on this board, and it's a fine place to start.

People are also a lot happier to help when you demonstrate that you've at least tried to research your question first. No one likes to have to spoon feed people answers to questions that could've been avoided with a Google or board search. Posting a question someone posted a hour earlier (and someone else posted yesterday, and so on...) is a surefire way to get flamed.

Your Apple apps will be fine post JB, and you update them the same way you currently do with iTunes. Just don't EVER update your firmware until you know it's safe to do so. Wait until the Dev Team gives the go ahead. Otherwise, you'll kill your jailbreak.

As far as what you want to do: Themeing can be very easy--prepackaged themes are available on Cydia and can be implemented easily through an app called Winterboard--or it can be as complex as learning how to create or edit your own code. I suggest starting with the prepackaged stuff; if you actually like mucking around with the file system on your phone, you'll quickly move on from the packaged themes. But the nice thing about using them is that you can typically install them without fear of borking your phone in some fashion. When you're first starting out, that's a plus.

As for text sounds--there are several options. Some SSH replacement sounds onto their phones. Others use apps. I personally went with BiteSMS. In the current Beta, you can use any ringtone already on your phone without changing file types, and can assign it to any contact on your phone. It's also got a lot of terrific features like Quick Reply and Quick Compose, which means I can text without leaving whatever other app I'm in. Easily the best app I've bought ever, App Store OR Cydia.

Hopefully that will give you a start!

 

The JB process was pretty easy although not sure how the new JB will be applied. I'm a first timer JB'er so I was a bit worried about doing the whole process. Thought I would break my phone or something. BUT, after having done it, no intention of ever going back to a stock iPhone again.

Like the previous poster said, read up on JB'ing. While it's not "hard" by any means you'll need to know what you're doing in order to make sure you don't brick your phone. Just take some time to peruse the forums here and pretty much any question you have has already been asked/answered.

All of your App Store apps will work fine and you can still continue to sync with your computer without any issues. There are a couple "need to have JB app" threads on here so those will break down what you should look into getting first. If you're a big texter, you'll probably want to get BiteSMS. It's basically how text messaging on the iPhone should've been. There are tons of Tweaks that will allow you to do a wide range of things. DisplayOut is a nice one too and this one allows you to connect a monitor to your iPhone. Downside is you'll need to get an iPad VGA cable but that can come later.

For layout purposes, I'd recommend all the "Infini" apps. There's Infiniboard, Infinidock, Infinifolder, etc. Really nice handy apps to have IMHO.

Since you'll be looking to change your ring/SMS tones. you'll hear alot about SSH'ing things into your phone. This might be a little confusing at first but, once you get the hang of it, it's easy to manage. If you need something a little more n00b-ish to start off with, you can download this. It works the same as your Finder/Explorer on your computer/laptop. It works on JB and non-JB phones alike and is probably the simplest way to add/remove files on your phone. So with the custom tones you want to change, all you'll need to do is locate them on your phone and replace.