USE A RELAY FOR EVERYTHING!!! only if you care about your truck burning down! atleast for moderate and high amperage accesories... then you don't need such thick wire under the dash, or such a heavy duty switch to be safe.
you can use a 4 or 5 terminal relay, in the case of a 5 terminal, you just don't use one. 5 terminal seem to be more common.
find a power source that is switched with the ignition (so you can't leave your lights on and kill your battery). you can wire it two ways, have the switched ignition 12V to the relay, or to the toggle switch. i can't think of a terribly strong aguement either way, as long as the existing circuit has an adequete rating. if you aren't on a fused circuit already, install an inline fuse.
it is not nessecery to go straight to the battery for your main power supply, you can use power from a distribution block on the firewall, it looks more professional.
i would use 14 gauge wire for the hi-amp circuit (feeding the lights), and 18gauge wire for the low amperage side.
relays are quite simple, although they can be confusing at first. think of it as a remotly operated switch. you use low amperage on one circuit to complete the high amperage circuit. do a google search for "wiring a relay" or something to that effect, and you will find many great diagrams. as we all know, a picture is worth a thousand words.
further more, if you have a spare 12V battery, some test leads, and a continuity tester (a digital multimeter), you can bench test a relay to understand what happens, it helps to take the cover off so you can see the coil enegizing and changing circuits. some relays aren't meant to be taken apart, so you may actually wreck the housing to see how they work.