I did my first tri last year and had exactly the same worries as you.
I put a estimated swim time of 15 -20 minutes so was scheduled to start quite early. There were many people including me using a wide variety of swim strokes.As it is a pool event you will have no worries about wetsuits.
There were many types of bikes being used from cheap mountain bikes up to high end tri bikes.
As I had a early start time there was little worry of me finishing on my own as the faster runners all started at staggered times behind me.If I looked at the finish list I was near the end but I had the satisfaction of being able to tell people I had completed a traithlon which was nice.
Go for it and enjoy yourself.