I've been using the G13 since beta and in my opinion it is a must have for any game.
My advice for button layout, at least initially until you find your own preferences is as follows.
Direction controls(strafe, forward):
Bind to the thumb joystick, this clears up every other finger for hotkeys.
Quickbar:
I prefer to match this up to the on screen layout. I key G1-G6(1-6) and G8-G13(7-=) as the left side of your 2 main quickbars and then do the same with the right side but with a shift modifier bound to your mouse. Shift+G1-G6(Shift+1-6) etc.
These initial basics can let you walk into any class and easily have 24+ hotkeys with zero thoughts and without having to move your hand from rest position or your fingers more than a half inch.
MIsc: Jump,Esc, Map, Inv , Crouch, etc,
I find the placement for these to be most efficient anywhere on the G17,G18,G19,G7,G14 keys, mainly because my index finger is by far better at stretching and building muscle memory.
The two keys beside the thumb joystick, G22, and clicking down the thumb joystick you would use for whichever you find most critcal. I use one of them for the map since I am always pulling it up, I use the joystick button for crouch on my Agent..these are the keys you should really tailor to your playstyle. Of course this is the most basic layout and you have the potential to set up very unique and comprehensive profiles but I have yet to find myself ever lacking for more keys.
I haven't found the need for a naga mouse now that I use the G13 though I do recommend a mouse that still has a few customization keys. Shift modifiers, push-to-talk, target friendly/enemy.