Introduction To Rooting - Read this first before proceeding

Sounds about like my usage. Its more about "feel" than usage, though, as long as the critical things function. I'm pretty sure 4G works on CM7 so I'd say that yes, it probably will work for you. I do use a different theme, though, mostly because I like the gauge-style battery as opposed to the bar icon that the stock CM7 comes with. The theme I use is called Mixer, which themes several different parts of the system. I also use LauncherPro instead of ADW Launcher, which CM7 comes with. But again, that's all "feel" sort of stuff. I just prefer LauncherPro over ADW for several reasons, the least of which being having 3 icon "trays" at the bottom that scroll and being able to use my own personal icons that someone made for me.

Give it a shot, though. The good thing about rooting is that there are a whole bunch of different ROMs available and if you don't like one, it takes about a minute to flash another one.

Sure thing. Don't be afraid to try other ROMs, too. I usually try to give each one a couple of days to see if I like them, but sometimes I know pretty quickly if I don't. You might want to consider trying different ones, Sense and non-Sense, just to see which you prefer (if either, I personally don't care, my taste is more based on how it feels and runs than what the underlying system is).

Some to consider trying are Myn's, Vaelpak, MIUI (which seems to me to basically be an iPhone clone but has some nice features), Fresh, and others. You can find discussions about them on the XDA link I gave you so you can see whether you want to try them or not, what they look like, etc. Make sure to read up on what each one has, as some have issues with SMS, 4G, and other things. Also, again, make sure you know whether its a Sense-based or AOSP before you flash a new kernel. Also, some are Froyo-based and some are Gingerbread-based. Make sure you check if that's something that matters to you.

Yes, you can. By reading the stickied threads in this forum.