Just remember that its not really watts that will determine how many lights you can run, it is amps. THe conversion for watts to amps at a constant voltage is watts/volts=amps. SO in your cass a 35 watt light at 12 volts draws 2.9 amps and 55 watt light draws 4.5 amps. A relay is only necessary if your amp draw is more then half of what your switch is rated. In my application and a few i have done for customers i use a high amp switch and leave out the relay. i use 12-14 guage wire also remeber that length of wire and amount of conections will increase resistance in the wire and in turn draw a few more milliamps. I always solder my conctions and use heat shrink. I hope that helps you out.
