In reply to Tall Oak:
What an excellent undertaking. Jolly good luck to you. I've walked parts of it, but more as part of general walking rather than an attempt at the whole route if you follow my meaning.
Always fancied doing it though, it would be great to hear how you get on.
I'm sure that you've seen it already but the following might help with the trip planning
https://www.breconbeacons.org/things-to-do/walking/the-beacons-way
When are you planning on doing it?