Return to training after 12 month break

Hi, my names Jack. I am a triathlete from the UK. I have taken a year out to go travelling which has been amazing, but all good things come to an end right?!

We will be returning home in June, and I will have a CTL of approximately 0 haha!

A bit of background on me. I swam and ran competitively in my youth, and cycled road & MTB. So i have a bit of a background with my sports. A severe illness took me out of sports until 2018 when I started to ride my bike again and did my first triathlon. I was able to slowly build my fitness, and spent a considerable time building strength in the gym. Lockdown was good for me as I buried myself in turbo work, and built on that once lockdown over. I basically took my 2018 sprint tri time down 30 minutes to 49:53 in 2021, setting my best 20 minute power of 360w (@80kg).

My goal is to get back there - and “transcend my limits”. I want to be able to dominate my local tri races, be competitive at TT’s, and work towards representing GB.

My question to the forum is regarding how to make a start. I want to have the best chance, even if it were talking 3 years to get there. Starting in June is awkward because it’s obviously mid season and the Joe Friel / Training peaks periodisation would not really work for me (as it’s race - but base I need!). In podcast ep 121 the talk is about building the best engine and it’s something I’m really keen on. Jim Miller says for a junior the first year would just be base, alas at 27 junior I am not.
So the crux of the matter, I can happily commit to Zwift’s active off-season of 12 weeks 10 hours on the turbo, but that would be great in winter and not mid summer!
So I would like to know people’s thoughts - go for a base plan in June, then repeat again over winter before building again, or maybe some kind of threshold improvement plan June - winter then work on base conditioning over winter?
I’ll have between 10-20 hours a week to train.

Kind regards,