What advice would you give to a triathlon newbie who has entered a 70.3 next summer?
Join your local club!
You’ll get so much help and advice from the more experienced athletes in the club, to help you avoid all the common pitfalls that we have all made in our earlier careers. You will also find the motivation and social environment of training with like-minded individuals will spur you on. You can find your nearest Welsh Triathlon club here: https://www.britishtriathlon.org/clubs/search?region=11
I would also recommend entering one or two practice events over shorter distances than your 70.3, just to get the hang of some of the nuances of event day and preparation. And practice your race-day nutrition in some long training sessions before the event, so you know how much you need and what your stomach can tolerate.