Well, you can make your own call, and if I were you I’d not worry about XP. There’s plenty of opportunity in Early Access to achieve maximum level without taking particular approaches to these quests.
Personally, on these questions:
(1) In my druid playthrough I convinced Kagha to turn away from the Shadow Druids, which is a viable way of completing the quest. But some druids might equally decide that she is turning against nature by attempting the Rite of Thorns and kill her if they can’t stop her, particularly if they’re not aware of outside influence. Or they might decide she’s right to protect the grove and side with her against the tieflings.
If I decide to convice her against shadow druids and accept the quest of her assasination, will i received exp and gauntlents from Zevlor?