I'll add to all of the above the Sea Otter is not a good race to pick as your first. It's a brutal course and it's a big race so it attracts a lot of stronger people. It also gets a lot of strong mountain bikers doing there annual cat 5 road race
There's nothing like a pro mountain biker stringing out a rapidly disintegrating group up the climb and then descending with a bunch of noobs through the corkscrew.
Do not do Sea Otter as your first race. It's a lot of fun, and much more so if you're not riding by yourself.