If your strongest sport is swimming, then you already have one up on most people doing tris! That's where most people struggle the most. And if you're confident in the pool, and can confidently close your eyes and still swim in a somewhat straight line without freaking out, and can occasionally lift your head without getting all disoriented, then you'll be fine in open water. My first open water event was a half ironman, and it went well. I went out and practiced the swim in the open water the day before the race just to get the initial panic of being in open water over with. So for race day I was good to go.

For the bike portion - just keep up your riding. You only get better with more mileage you put on your bike. The speed will eventually come and work in some speed intervals occasionally which will help your overall mph in the long run. For the running, do what you can. Remember - you can always walk a portion if you really really need to. And again, speed intervals in running helps your average speed increase over time!

Welcome to the triathlon community! It's a fun sport and will kick your butt into great shape! And if you're a little concerned about the event (having to walk, etc), sign up for a women's only event - they are great - fun and supportive atmosphere like no other I've been in - women cheering on fellow women triathletes even the last one through the finish line. I did Iron Girl last year and it was incredible.

If you have any questions or concerns, never feel like any question is a stupid one - they are all valid, especially b/c triathlon can be intimidating at first b/c there's so much to find out and know (what to wear? when to eat? where do i put my bib number on? etc etc).