How to go about controlling and powering 4 x 120mm PWM Fans

The transistor is not necessary. The Uno can drive the PWM pin directly.

For an initial prototype, a breadboard is the best way to put it together. Buy one of these at Sparkfun[/] along with the matching breadboard and some wires and start playing. All of these are included in most starter kits.

For permanent use, transfer your design onto a proto shield instead of bare perf board.