You need to make a nandroid backup. That means installing Clockwork Mod Recovery (CWM) or TWRP. I used to use CWM, I use TWRP now and prefer it because of the interface. (They both make usable backups - but I've restored ROMs a few dozen times with TWRP and I feel comfortable that it will work if there's enough free space to make the backup.) You have to choose one or the other, though - one can't read the other's backups.
Then you just back up the ROM, flash Cyanogen, if you don't like it, try flashing some other ROMs and, if you decide that the stock ROM is still the best, restore it from the backup. If not, keep the backup somewhere anyway. You may change your mind, or you may want to sell the phone, and the buyer prefers the stock ROM.
I'd also, after making the backup, but before flashing anything new, back up all my apps and data. Email and contacts (if they're entered as Google contacts - they all should be) are backed up on your Google account. I use
Helium for app data backup (if the phone isn't rooted, it'll tell you to download a file to your PC - do it. That file lets Helium work on a non-rooted phone),
App Backup & Restore to back up apps (you can install an individual app from its backup, even without AB&R installed - which makes it easy - you back AB&R up with your other apps, restore that first, then use it to mass restore whatever you want.
SMS Backup & Restore for my texts. Everything else I drag&drop to my computer. (And, of course, all the backup folders from the above apps. BTW, Helium's folder is named carbon, for the old name of the app.) Then I drag
that folder to 2 cloud accounts. (It's not paranoia - having too many backups is like having too much money. In order for me to lose all my backups, about half the world would have to be destroyed. Remember, a computer or phone can be replaced - some data can't. [Your first child will never take his/her first steps again, so that video is worth more than mere money.])
BTW, all you sound like is an intelligent person who would like some advice to do something he doesn't know how to do. Now, while those of us who were born knowing everything can't understand that ... seriously, about all I can think of to fit that *** is "newcomer" or "noob".
Oh - if all you don't like is Sense, try
Nova Launcher. It's just installing an app, so you don't have to do all the above. It basically replaces Sense. (Let it get its data from the original launcher when it installs - your choices are to install with nothing on the desktop or install with the apps and widgets you had on the original desktop.)