Your first cat 5 race
I don't know where you are located, however, if you're racin' in Cali or Colo for that matter, no matter what kind of shape you're in, your strategy should be to finish, with or without the pack. Fitness is a part of the equation. In LA where regional or national class triathletes moonlight in the 3s, 4s and 5s, fields are large in the 5s, 50+ on a tight course, 100 on others, 20 somethings who think they're invincible are everywhere, new racers who are bound to be 3s by the end of the season are off the front on the first lap, good solid guys who are on steady Friel diets are right there, racing is downright tough.
Do you know how to corner? If not, please find a local racing oriented club or a coach in your area to help you out. Find a 3 somewhere that you know to practice a little countersteering with, wheel rubbing, shoulder bumping, wheel protection, etc. When I was a 5 back in the day, things were really quite rough. I was extremely aggressive just to keep the squirrels away. Nobody took a line inside me if I were taking the inside. Nobody gonna sweep me out, no way. That's the worst part about the 5s. Nose divers who get inside over their heads and can't hold line.
I would say on average, there was about one or more crashes per race. Survival is the idea.
Good luck, have fun.