Beandip is right...I use the Radio Shack solder station that has a 20 watt and 40 watt heat range at the click of a switch..The 40 watt works good for soldering your grounds to the back of the pot and the 20 watt is good around the other wiring to the switch,pot terminals etc..
If I had to buy just one iron though,I think a 30 watt would work...