Hi Tom
I'm thinking of walking Glyndwr's Way next year, but starting on Offa's Dyke with my first overnight at Llanthony. The Priory has rooms and a pub, fantastic place, I would highly recommend it or the B&B across the road. From there, its an easy walk to Hay-on-Wye. I have the same agenda as you, nothing over 15 miles and preferably less.
Good luck in your planning.