Are we going to be fighting single legendary monsters most/all the time or will there end up being other creatures in our fights?
How are HP calculated? Full HP/lv since you're lifting rules from SirP, or something else?
Anyway, build stub:
Centaur3, Something2, Paragon8 // Spellshape Champion5, Oracle of the Stars 8
Khan for the Centaur path, Astral Essence, Glimmering Moon, Brilliant Dawn (probably with emphasis on the first two) for circles. Paragon Ability for an excellence, also probably toughness. May well brew up a greater excellence that's an improvement of paragon ability. The ability in question would be the Oracle's Cryptic Astrology.