Advice for an android beginner?

Lately, my iPhone 5 has been starting to crash a lot, and I've always hated battery life, as well as the fact that my lock button rarely ever works.

I'm quite locked into the iOS ecosystem, with music and apps i've purchased, but i'll be picking up the new ipad mini this fall to fill my iOS needs

Therefore, i'm looking into picking up an android device to use for the foreseeable future.. most likely the SGSIII (I don't need the S4, considering i'll only be using it for a year or so)

I love the look of stock, so i'll be installing CM, although I have no idea how to root or even install this. If anyone could lay it out for me, it would be greatly appreciated. :)

If anyone knows of where I can find an SIII for a good price, i'll buy refurbished. Thanks in advance, googleplex!