3 questions SOS

2. If you are working in larger scales, I guess the best thing to do is to drill out the inside of the headlight, paint it silver, then cover the headlight with a lens made of something. That something could well be transparent plastic, or elmers glue or krystal klear. I find that using Elmers gel glue (blue tinted) is perfect for that sort of things. It dried extremely transparent and thin, and stretches over the surface to be covered. For smaller lights and smaller scale, a bit of driling out, some silver paint and a blob of glue is just fine (for me).

3. It's a matter of preference. Some people also add some green. I just use black and white but often use a different mix for a wheel or two, just to give a different shade from other tyres. Having said that, it's not often that you can actually see a difference once the washes, the drybrushing and weathering have been done!

1. I do not know for sure, so I'll let others tell you!

most armored vehicles don't have true headlights like cars. They have metal covers over them which only allow a limited amout of light to shine through at a downward angle, hence the lights would be painted the vehicle color .
on wheels, the rubber should not be gloss black, most would be dirty, i just paint mine flat black and then dirty them up after assembly along with the rest of the vehicle for my weathering effect

Another way to do headlights, if you want that realistic rounded look is to check out a company named M.V. Products. They produce many sizes of lenses with parabolic backs done in silver with rounded glass fronts. They look very good, and people in the model railroading scene swear by them. Give them a look see.