You will gets lots of good advice from the tri vets here, but here is my 2 cents.

Last year in a 6 hour adventure race(no swimming, but paddling so think wet butt), I wore tri shorts and a full coverage bra top.

This year for my triathlons, I purchased a tri suit. I will do all three disciplines in the suit. I did not want to have to think about clothes at all during the race. I will wear it under my wetsuit, strip and go...like hell I hope!