Go for it and have a go.
Trackdays are seriously good fun and very addictive. Most trackday organisers are serious about safety and driving standards, they won't allow you to mess about with handbrake turns etc, but you'll be having too much fun without messing about with your handbrake.
No serious expense is required - a good helmet is needed but most good trackdays have them for hire, make sure your brakes and tyres are in good condition and you have had a recent brake fluid change otherwise you'll boil it and ruin your day, no loose items in the car, and make sure your cooling system is free of leaks and in good condition.
Apart from that just go along and enjoy yourself.
A safety talk on track rules and driving ettiquette will be given so you will know what is expected and allowed. Most track day regulars will welcome you along and give you tips and encouragement, and as long as you abide by the rules and move out of their way to let them past will not care what you are driving or how fast or slow you are.
A good smooth fluid style will make you quicker than trying to go too fast and being out of control. Most trackdays have instructors that will accompany you for a small fee, and their advice will make you a better, quicker, safer driver.
My 19 year old daughter has taken to trackdays like a duck to water.
Give it a go and have fun.
Cheers
Paul