The pockets on the tri top are angled for easier access while running and to decrease the amount of bounce you get from having something with some weight, like a gel in there. That significantly decreases chafing. The anlging also allows the seams to move with your body better.

I never wear my race number on the swim, this is why the race belt is so handy. It allows you to snap your number on very quickly and securely for the bike and run. Many races still require you to wear a number for the bike and that one is supposed to face backward, the run number faces forward. So it also allows you to just spin the number around at T2.

Definitely get a light mesh hat. Triathlons are terrible for over exposure and once that helmets off you lose a lot of coverage.

I would also recommend a one peice tri suit if it's a shorter race.