I would like to chime in, since I started out as a triathlete, even though I have been running since I was 19 ( free running, no special type of training or racing in my younger days).
Positives: You have a big running foundation, so that will help you out a lot, because a lot of triathletes suck as runners. But you have the knowledge, speed and form to put you over the top in that area.
Negatives: Swimming! I've been swimming since I was 9 years old, and it still took me a while to get acclimated to OPEN water swimming. It's an entirely different space. The pool is very calm and temperature controlled, so there aren't any natural forces going against you. However, in open water, there are many forces that you have to endure. The water moves three dimensionally, creating a hard resistance that you have to propel through, plus the water is a lot colder, which will have a certain effect on your body temperature. You want to get in a lot of practice with swimming in open water before you attempt to do your first triathlon. Many have not survived the swim, and some have any died during the swim because it was too exhausting, or hypothermia set in, and they drowned because of it. 90 percent of the deaths that have occurred during a triathlon happened during the swimming stage. So take it seriously, be prepared, and don't endure it until you are 100 percent comfortable.
To me, biking is the easiest part of the triathlon. An athlete can coast on a bike, and pedal sparingly to preserve energy for the run. You already have cardio strength, so building up muscle memory for cycling shouldn't be that hard.
I stopped doing Tris because I'm a runner at heart and body( my second love wold be swimming), and I just didn't feel like an athlete because there are so many POSERS at triathlon events. Don't get me wrong, it's a tough sport, and there is a lot of fitness involved, but it just comes off as more of social sport. Plus, the transitioning and bike transportation are just too complicated and cumbersome. You have to haul a bike around, and certain mechanical failures can put you out of the race. That's just too much of a hindrance to me.....Also, it is very, very expensive.
However, if that is your passion, be the best that you can at it.