Hello - I am just getting started

Well I am defiently new here. I am excited to say that I will be competing in the St. Anthony Tri on St. Petersburg FL. I have been working out but I need to step it up. I have been reading a lot of the informatio on this site to better help myself train. I think I am going to use the 16 week Olympic - 3x Balanced workout. It seems to be the most appropriate. If you have any suggetions please pass them along. I have a background in gymnastics and track but I was a sprinter. I never ran long distances. I am also a certified scuba diver but I am not experienced in distance swimming. Right now I seem to be having the most difficulty in my flexibility. When I run my calfs get very sore. I have been taking it easy and stretching very well everytime I work out. I am in great shape right now but I do not have the endurance yet. I will take any advise. Thanks,

Lori