Hi Michael,
I'm running stock wattage in the car without relays, and really big stuff in the car with relays (130/100w H4 and 100w H3). With no relays, stick with stock wattage bulbs, otherwise you'll stress the wiring harness, headlight switch, and - in the case of the fogs - blow fuses. The ultimate stock wattage H4 bulbs are the Philips Vision Plus, the "+50" bulbs, from Powerbulbs.com.
Most bulbs are designed to run at 13.5v (I believe). Typical older Mercedes alternators (before the mid-90's) put out 13.6v or so, which ends up being 12.x at the bulb connector (at best). So if you can get ~14.2-14.5v with an adjustable regulator - under load - that will help a LOT, especially if you don't install relays. Don't forget to test the regulator setting when stone cold, where it will be the highest! You don't want to set it hot at ~14.5 and then find out it puts out 15v+ when cold and blows up electronic stuff.
I'm about to attempt an upgrade to a 143A, 1998 S500 alternator, and I'll be doing some before & after testing on voltage drop under load etc & posting the results on the forum.