Default Newbie looking for some guidance

Hello fellow members of XDA,

I am new to this whole thing of rooting and installing custom rom, so I’m kind of overwhelmed. I have done some poking around prior to this post and stumbled upon the Sticky and was wondering if the “[REF] [GUIDE] Welcome to your device, the Galaxy S III - by theexel” is this the standard to what I should be following?

I have a T999 on 4.1.2. I appreciate your time, recommendations, and advice that you have to offer. Thanks!

I was hoping you could answer some questions I have for Sanranhai's stockMod 4.3. If i followed the instructions while flashing the rom + one of the modems I'm still able to go back to older roms correct? Also if i decided to cmw restore to my backup (4.1.2 image) will the modem be the one I flashed from saranhai's or will it go back to how it originally was before? Thank you for your time.