Hey man, I've got a XT905 so hopefully I can help out.
1. I rooted pretty much as soon as I got my phone. It was on 4.1.2, stuck with all the Telstra and whatever else bloatware so that's what made me go for root. I used (back then) motochopper to get root, and then motopocalypse to unlock the bootloader. Both worked without a hitch and it's been smooth sailing since!
However. I've been re-reading through the threads lately, and, if I understand correctly, it looks like the exploit motopocalypse used to unlock the bootloader has been patched, so that doesn't work any more. I've been reading that geohot's new root for the Galaxy S5 works for the RAZR M though! So maybe have a read and give that a go.
2. I decided to keep it at stock, because all the ROMs on offer all had some problem with them, such as audio, wifi, camera not working, etc. What I did instead was install the Xposed module + Gravitybox, and it pretty much lets me control a lot of functions of the phone. I also used TitaniumBackup to freeze/uninstall all the crapware, and finally a launcher to get custom homescreens.
Hope that helps a little, good luck with rooting your phone!