Most of your questions are sort of American specific. We are all in Australia. Most of the brands for oils, coolant and headlights will be all different. And we can't help with your busser either sorry. Hit it with a hammer.
Some warning. The aftermarket car "tuner" is easily misslead with brands and advertising. You don't really need anything Toyota didn't suply on the GT-S model, except shocks, coilovers, and suspension bushes/joints. Everything else, replace with stock new item.
Oil brand makes no difference. Use any old gear oil or even dextron III in the gearbox. But don't use a 90 weight as it's too thick. Use any old diff oil in the diff that is GL-5 or better. Use GL-6, GL-5* or LS90 if you have a LSD. For engine oil, use anything. Get it cheap at the supermarket. It will make little difference. Change the engine oil a lot. The diff and gearbox does not matter, as long as it has oil.
For coolant, I like genuine Toyota coolant which is red. It protects the system well, but will leave a pink crustation mark where it has leaked or overflown. Don't mix with other coolants.
Headlights, ebay. H4 conversion kit.