I worked myself up about fighting elder and then steamrolled him. You'll be fine. Just bring the best bow available, fully upgraded, and a couple stacks of fire arrows. Pop Eikthyr power at the start. Use pillars as cover from his ranged attack and rotate around pillars to avoid his AOE ground effect.

As for finding swamps, they are always on shorelines so boat exploration is the ticket. Do permimeter runs around islands and you'll find some. I believe they will only generate a certain distance away from center but it doesn't seem to be that far.