So I bought a ticket to this event next month at Origins. Can somebody tell me stuff? Also can I bring my own deck (Rex) or will I have to use what they give me? I can bring only zero level cards.

This doesn't appear to be related to FFG directly

But from http://originsgamefair.com/events/#ccg

Quote

CCGs/TCGs (Collectable Card Games/Trading card Games)

This type of game is played with a pre-constructed deck of specialized cards. There are also sessions of this game in which cards are given out in booster packs, and a deck is then constructed from those cards.

Otherwise try and ask here: https://www.facebook.com/originsgamesfair/