So! It's as the title says. I'm looking to upgrade my headlight bulbs as the second-cheapest option to improve visibility (which isn't nearly as great as I'd like, even after attempting to restore them).

Now, I'm still extremely new to cars and I can only Google so many things. I got this car used, without a manual, and I'm struggling to figure out how many bulbs I'd need to get, what types, and if there's really a difference between the high and low beam bulbs.

So:

1) When replacing bulbs, will I need to replace low, high (is there a difference?), and fog light bulbs?
2) Would I be able to use xenon bulbs, or should I stick to halogen?

 

Assuming you have the euro halogen lights and not the american sealed beams...
The wiring is for 60/55w H4 main and 55w H3 fog lights. I've heard people complaining about 100/55w H4 upgrade has burned out their wiring, but I've had these in mine for a few weeks without trouble, they're not very expensive globes. I previously had a pair of blue tinted 60/55w that were brighter than stock just because the whiter light penetrated better than yellowish stock light, they didn't have increased candlepower or anything.

There is a Phillips Extreme Vision 60/55 +100 (claimed +100% lighting over normal halogens) which has good reviews for increased brightness without stressing the wiring, but these are expensive globes. I believe they could be xenon-filled halogens which is a hybrid, and they're also slightly blue tinted for a whiter light. These I believe have increased candlepower over stock but run the same wattage.

A full xenon conversion requires other components like resistor boxes installed so they work properly and they're unroadworthy in most places unless you have self levelling headlights installed (late model cars with factory xenons have this). People do it and you can buy them in kit form for a halogen conversion, but they may not be legal in your area.

If you find the stock high beam is completely inadequate a bulb change isn't going to help very much, it's the beam scatter caused by the unit reflector, which is designed for a broad beam to light up a wide road area in front of the car. What you really need is a pair of focused-beam driving lights bolted under the bumper, these will penetrate much further into the distance. These in 100w will be twice the lighting of a 100w high beam in the stock headlights and will make stock 60w high beam look like low beam.