Looking for guidance topic

I am fairly familiar with rooting and such, but I am currently lost. I just received my hdx (thor) and have it rooted with a custom recovery and a stock backup. But, my question is, do I need to be on certain versions for certain custom roms? I'm currently on 13.3.1.0. Would I need to download/install a more recent version before I can began flashing?

Thanks in advance

[Q] New guy looking for some good guidance topic

Ok so I got into this because I got a spare phone from a guy that tried to root and install custom rom but couldn't get it to work and had thought he had bricked the phone. The phone still worked but would not display anything so I used adb and installed multirom recovery and then flashed I believe the fluent lollipop rom. got the screen to work and added a secondary bad boyz rom to install. What I want to do is find a good beginners guide on what a Kernel is and what to look for when changing roms and kernels, would like to try CM12 lollipop so would need to know which recovery to install and how to uninstall the multirom, and would like to just find a straight forward breakdown of how this works. thanks again for any teaching I can gain from anybody.