Stupid H4 headlight question
I'd supply the relays with a 10AWG wire directly off the back of the alternator (using a 20A circuit breaker for protection).
I run 80/100w H4 bulbs in my truck and love my "deer huntin' lights". Due to the superior beam pattern of a GOOD H4, dazzle of incoming traffic isnt an issue. Just aim the lights correctly and you should be fine. But on high beam, reflections from road signs might actually hurt your night vision, so dont go too nuts on the wattage.
Beware however of some of the H4 lamps out there. There are some that claim to be "Euro" which are illegal here as well as there (but you would be far more likely to get ticketed for driving with them there). The "diamond cut" crap as seen on eBay is a prime example. Also some "E-code" lamps may be for the UK where they drive on the other side of the road. Check out
http://www.danielsternlighting.com/tech/lights/codes/codes.html
for an explaination of headlamp codes.
And yes, H4 lamps typically are not DOT approved. 9003 lamps are however, and basically the same. A good H4 setup is a safety improvement, as long as you stay away from colored bulbs and other such detritus.