I'll start out by saying that Sense based ROMs are, in general, the largest files. For instance:
BAMF Forever 1.11 is 310.8 MB
Thunderstick Full Blown is 338 MB
Infected Eternity is 383.3 MB
And then comes the Desensed ROMs, which are stripped down versions of Sense that use a Launcher:
Bully Desensed is 239.7 MB
Accense is 178.2 MB
Followed by CM7 based ROMs:
Thundershed is only 99.6 MB
Liquid Smooth 3.2 is only 70.1 MB
So, that shows you that some ROMs use more resources than others, and "I" think it's noticeable in the performance/lagginess of the Bolt. The No-Sense and De-Sensed ROMs use Launchers, and again "I" think that some are better than others and make a difference in performance. For instance, Thundershed comes with Go Launcher, which I don't like, and it comes with all of the Go Widgets that you have to download. I prefer ADW Launcher EX, which has optimization settings, plenty of customization options, and none of the annoying widgets to download. However, many people LOVE Go Launcher, and you might as well, so give it a try before you decide if it's the right Launcher for you.
Every ROM comes with certain apps preloaded, but in most cases, you should be able to uninstall them if you don't like them. Cory was nice enough to Pin a thread in this forum that gives you a rundown of which apps are okay to freeze and how to do it:
http://forums.androidcentral.com/th...-rooted-how-put-them-back-11.html#post2093944 That should give you an idea on what is standard and necessary.