Hello Richard, and welcome. I hope you find the path of the bard inspiring and rewarding, I certainly did. Some of the answers to your questions will also be found in the Bardic Course materials as you progress, however, I have some ‘answers’ for you, too.
The Golden Dawn traditions are based on late 19th century Western Esotericism: Hermetic and Qabalistic currents that developed out of Renaissance, Judaeo-Christian, Neo-Platonic, Gnostic and Classical (Greek and Roman) ideas based on a Masonic framework. They certainly are traditions with a fine pedigree, but, in spite of the Welsh names, all that ‘Celtic’, at least in my opinion, they are not.