Oh the famous what should I get question!! Hehe j/k
I bought my TRex used and it was a CDE converted to a SE minus the main bearing blocks. If you can afford it I would suggest going with the SE version because you're going to want to upgrade to a metal head and tail anyways so you might as well knock it out.
As far as any other upgrades to the SE version I would just recommend getting a set of Gorilla Gear and definitely Rdlohr's (on HeliFreak) under gyro mount. It keeps your gyro safe under the frame and out of the rotors path!
I don't really have much experience with other ESCs and motors so I can't provide input there... but I do suggest holding back on pointless bling (canopies and such) and getting as many batts as you can (you'll thank yourself in the long run) There are alot of choices...but for just starting out and hovering around the new Apex 2100s are a good deal.
Another experience I learned with electrics is you either need an ac/dc charger or a dc power supply for your charger... I started out using an old car battery... but it got real annoying real quick. I converted an old PC power supply and it works perfect.
Keep us posted on your choices and take some pics and vids.