I don't have a lot of advice to give, but I'm planning to do my first triathlon this summer too! One thing I'm hoping to do is to join a triathlon class that my local running store is putting on - it's expensive, but includes group workouts, training plans, coaching and the entry fee into the event. I really feel like I need someone who knows more about it than me to be there when I have questions
I'm also lucky to have a few colleagues who do much longer triathlons and have offered to give me advice about things like transitions. Is there anyone you know that's done it before that you could go to for help? I'm also trying to remember that it's okay to be slow - the goal for my first one is just to finish, even if it's much, much later than everyone else!