SUroot helped me out quite a bit in my leap into the rooting world. It wasn't difficult, but ensure you take your time, and follow the steps absolutely to the t.
As far as ROMs, I'm still in learning mode; but I've read up about the different categories. Personally, I'm not fussed on the look of it, as you can customise it. Battery life (which I'm still battling with) and speed were my main wants in my desire.
I was given this link to the different ROMs by the lovely jimeller;
Desire Index - Everything Desire is here! [UPDATED: 11/4] [Finally! Some Statistics!] - xda-developers
Worth a look.
AOSP (Android Open Source Project) are ROM's which are basically the bare essentials (correct me if I'm wrong anytime!). Sense isn't on these, and it really is just vanilla software. Good battery, speed and reliability are the main points to these ROM's. I'm using Gingervillain, but there are a few different ones.
MIUI are ROM's that can incorporate other manufacturers interfaces, like Samsungs TouchWiz, Motorola Blur and even iOS etc. Apparently, due to the massive customisations of the kernal, these ROM's are a bit battery hungry.
Sense is what you already know; it's based on HTC's own launcher, and the devs are always updating them to be up to date with HTC's current offerings. I've read that Gingerbread's sense ROM's are still a bit buggy, so it's recommended to stick with 2.2 (FroYo) ROM's if you must have HTC sense.
This is what I've learnt so far, and again, if any of the above info is wrong, please feel free to correct it!