well 1st off welcome to 6gc >

> .
as for your questions:
check out coomers
6gc.net parts database links and pics to most of what you need to know for 6th gen celicas.
yes, there are a few bodykits that are very clean, on a 15-16 year olds budget a zephyr or combat kit are your best options. the other ones get rather pricey

(combat)

(zephyr/erebuni 404/ z-glide STYLE)
just remember with bodykits the price of the kit is only 1/2 the total cost, unless you have some good conections, the installation on a 4 piece kit will run you just about the same ammount as the kit itself, also ebay kits are a 50/50 chance so only bid if you are feeling lucky.
jdm headlights are EXPENSIVE... like 500-700 bucks for all 4. boibleu or john will give you an exact price that was just what i could remember.
there are no taillight "upgrades". if you are speaking altezzas then upgrade is the incorrect terminology. >

> personally i will be venturing into a little taillight cover/conversion from scratch over the summer similar to the JDM gangs jail kit, and someone, i think jason, will be doing a tricky RSX (correct me if im wrong) taillight conversion that we are all interested to see how that turns out. JDM taillights are pretty sweet and run you about 350 bucks.
hope that helps! later.