Finding a team with lots of women will be hugely beneficial to you. If nothing else, it will give you people to train with. If you don't already know of women's teams in your area, you can go to a local race (even just to watch) and see what teams show up and talk to the women of well-represented teams after the race.
To answer your question about speed, around here, cat 3/4 crits are usually an average pace of 20-23mph. However, keep in mind that this is average speed on the computer after the race. What usually gets people are the constant accelerations/surges. You will find yourself accelerating out of corners and accelerating to cover attacks and, of course, needing something left in your legs for a sprint finish.
Interval training aimed at boosting your LT, boosting your VO2 max, and boosting your top-end power will help immensely for crit racing.