I know a lot of people love the Aga Tiamat + (I do too, its one of my absolute favorite devices) but I highly suggest an original Phoenix Clone (not v2) to start off rebuilding. Its a great way to get started rebuilding and you can pick them up at LiteCigUSA.
Phoenix Rebuildable 510 "Dripping" Atomizer
12.95 will get you the Phoenix Clone, Screwdriver, 5 spare wick and coil assemblies, a pre-installed wick and a drip tip. This is what I started on and I highly suggest it to anyone else. It is a beautiful little dripper and holds quite a bit of juice.
There is a lot of problems that can arise from owning a Genesis style atomizer that are slightly more complicated than wrapping a coil on some silica and throwing it on the two posts. Though I admit they share similar problems almost all problems with an RBA is related directly to the skill of the person wrapping the coil and (in the case of SS Mesh) building the wick. Start off simple - get some experience, you will get frustrated! Do a lot of research, read a lot of reviews and watch a lot of videos. I probably read 50 pages of reviews and instructions as well as watching 20 or so videos before I even received my phoenix clone.
I got frustrated, I got upset, I was not as instantly inclined to building wrapping a coil as I expected to be when I first got it. However thanks to my experience with it, when I moved up to a Genesis Atomizer - First try.
Another great place (if your not looking to spend a ton of money right off the bat when you start rebuilding) is thehouseofvapor.
Rebuildables
Silica and Kanthal are extremely cheap here and sold by the foot. So if you don't want to spend 8-15$ on eBay buying 100ft of wire or more on silica (this place has the cheapest silica I've seen yet) you can go here. 30ft of Silica, 30ft of Kanthal is around 12$ shipped and will go a long way! They usually have a coupon code as well right now the code 'vf' works for 10% off your order. Unfortunately they are out of stock of almost all their silica
Best of Luck.