Definitely.
Hmm, hard to say just yet. At any rate, the goddess clan would definitely operate in the morally grey area; so far their revealed actions have only been against the demon clan, all of whom were never exactly nice in the first place.
I don't know about that. For one thing, Gowther's power was amped by Merlin during the vampire incident and Escanor hadn't been at his absolute peak at the time either. Plus how he more or less shrugged off Gowther's nightmare ability during the tournament Dolor and Gloxinia threw.
Way things are shaping up, I'd say the 'final boss' of the series will either be the Demon King or perhaps even someone from the goddess clan.