Have fun at the class! Your CBJ number should be the same as your KCBS membership number, unless they've changed. You're certified and ready to go the minute you pass the class. You can sign up for anything then, using the number. Just explain you graduated from class X on date X and you should be good to go. As far as random choosing of judges, that's up to the organizer. If they have enough judge applicants they may do it randomly or they may go with experienced judges only, but my wife and I didn't have any problem getting a gig right away. New judges are not treated poorly as far as I've seen in my young experience as a CBJ.
NB El Dorado Offset, Primo Oval Junior, Traeger Model 075 Pellet Pooper, Big Chief, Kingfisher Kooker 14" gas/wood combo, PBC Brethren Edition
Home Brewer, Murderer of Squirrels, Armadillo Inspector
Flaming Pig Head Mod
Black Thermapen, red backlit Thermapen
Certified KCBS BBQ Judge