Personally I have 4 skills + 2 modifier keys set up on my Logitech G600 the other 6 buttons just sit there because I don't like them and I am shunning them.
Have three hot bars for skills:
1: Healing skills - No modifer
2: DPS skills/Alternative rotation - CRTL modifier key bound to G13
3: Cooldowns - ALT modifier key bound to G14