We used Celtic Trails to book a self-guided hiking holiday in Wales, and I would use them again. But lately we have been going with HF Holidays for guided walking, so I heartily endorse Katy’s suggestion. We really like their accommodations, food, hikes, guides, and the company of other hikers, mostly in the 55+ age group.
On our last holiday with them, there was a group of 4 women, all restored academics, from Bristol. They took a liking to us, and we to them, and it was lots of fun.
HF Holidays is a member-owned cooperative, and their prices are very good. Non-members are welcome, with a small supplemental fee.
This is the opening page on their Wales holidays:
https://www.hfholidays.co.uk/destinations/united-kingdom/wales
Here is a complete listing of their Wales holidays, from 3-days to a week, coastal hikes and inland/hilly hikes, filtered for availability in October:
https://www.hfholidays.co.uk/holidays-and-tours#/holidays?dfrom=2024-09-27&dto=2024-10-31&FL.Location=Wales&sort=ordering%7CASC&page=1
Unfortunately, is appears they do not offer the coastal trails in October. I wonder if that suggests something about the weather? Perhaps too windy?
And this is the trip brochure for one of the 7-day programs in the Brecon Beacons, for an example:
https://www.hfholidays.co.uk/holidays-and-tours/7-night-brecon-beacons-walking-with-sightseeing-holiday?format=pdf&vid=3254