You absolutely do not need a gaming keyboard or gamepad. Most gaming keyboards offer macro's so they can help if you use or plan on using a macro and gamepads offer a faster learning curve.
Personally, I use a $12 logitech USB keyboard for all my gaming (Battlefield2, Battlefield 2142) becuase it was the cheapest I could find, and I do more than adequate, I can't remember the last time I've lost my fingering or had a negative KDR.
I would suggest getting a gaming mouse. The G5 has been replaced by the G500 and it's almost the exact same , it has some slight tweaks but nothing major. I recently picked up a G500 and it's great, the adjustable weights are fantastic (I love a heavy mouse), it's very precise and has an internal memory so you can save all your settings when moving to different computers. Comes with great software that allows you to program each button to your liking and create your own macro's.
Obviously, I would suggest the G500.
I actually have a spare, brand new in box...let me know if you're interested.