you cant
you can not get him in the game
yes you get it at an event.
The only way to catch Celebi in Pokemon FireRed Version was to get the special Pokemon from a event. The only other way would be to cheat using an action replay device with a code.
You get celebi from the new Pokemon movie as a door prize along with a shiny version of a legendary dog. Celebi unlocks an event with allows you to battle Giovanni. And the dogs unlocks an unknown event in the future Pokemon Black and White.
I don't think you can catch celebi at all in fire red. There is one way though bring your gameboy/ds with a wireless adapter to a Pokemon convention to get celebi.
It is an event
It can be any level.
You can't catch celebi in pokemon white.
yes
you can not catch celebi in Pokemon platinum
You Can Not Catch Celabi In Pokemon Firered Unless you trade with pokemon heartgold or soulsilver.
You'll need to transfer it or trade for it. You cannot catch it in the wild.