I spent a lot of years sailing Superior, but only once ventured down through the Apostles. I don't recall
balls outside of the town sites.
So yes to anchoring. I don't recall
the bottoms, but I'm pretty sure it's mostly sand/mud. I prefer a good, over-sized new-gen anchor like a Spade, Rocna
One thing, there really are no perfect anchorages
in the Apostles. You're basically anchoring in the lee of the islands, so you choose your side depending on the expected wind
conditions. Mostly we get westerly winds (as I'm sure you know), so anchoring on the east side is generally the plan, but you do have to be prepared to move around if the wind