New to ROM'ing

So I got a bionic the release day and I still have a DX in great shape..minus the 4g haha. I have been using it as a test dummy..I took the OTA then flashed back to froyo for practice in case there comes a time to do it for my bionic. Well now im going to try a little more...I want to install a custom ROM and i have a couple questions...

I know there are ROM guides so this isnt about how to do it its more about some "understanding" I am looking for...Here goes nothing

When i choose a ROM to flash to such as Liquid, liberty, MUIU, CYANOGENMOD ect...is there a version to flash to from each version OS? Meaning if I am on froyo is there a certain "froyo" liquid i need to use or if I'm on GB is there a a "GB" version of Liquid?

Secondly I want to know which ROM's people recommend...I use my DX for browsing, wifi tethering (needs to work), and apps....its kind of like an Ipod touch right now...not activated but i use it as a mp3 with games and access to the net, market, and email through wifi.

* i need the ROM to work with wireless tethering just in case i have to go back to that phone in the even that my new one takes a dump..

thanks to all!
I look forward to your help, information and opinions!