As one who is fairly new to RBAs, I have an AGA-T+ and an AC9 clone (RSST). The RSST is, by far, easier to setup and get going than the AGA-T+. I've been fighting and fighting with with AGA, but got my RSST setup and vaping clouds on the first try. It has a smaller tank than the AGA, but with the ease of setup and all that, I much prefer it.
As for wire diameter and mesh, check out Steam Monkey. I started out buying shorter lengths of 28, 30 and 32 and have built coils from all three. They have different characteristics and by trying all 3, you can figure out what you like and order more. I settled in with 30 awg Kanthal myself, but that varies from user to user. Steam Monkey also has great prices on SS mesh. Better than I've found anywhere else, in smaller quantities.