The opponent at the end of the temple is level 15, IIRC (uses Explosive Arrows, anyway, which has level 15 requirement to learn), so it would help if you were at least close (level 15 would give you access to spells like Healing, etc).

What Black Ring camp? The Black Ring takes over the quarry; you can clear the opponents outside and get a little loot, but will not be able to enter the tower until after taking over the battle tower.
The bandit camp (a little north of the quarry) has a few side quests you can do, before you report back the location and password (afterwards everyone is hostile).

When you finish off Maxos Temple you will get access to Sentinel Island. Your first encounter there you can mindread to go up a level, so the higher level you are the more of an experience bonus that will be. I made it to 22 in the fjords, with Broken Valley pretty much cleared (only a few quests left to turn in). You don't need to get to a high level, but it would be better if you got to a new level before entering, to get a full level bonus (equip anything you have with a Wisdom boost).