I'm not sure exactly. It's just one of the generic park recycling containers. I'd guess it's at least aluminum and plastic.

I would certainly assume so; mostly I was just adding it for the sake of the renderer so that it would properly visualize the stop direction.

This road has been abandoned for a few years now as the park has been undergoing renovation. The aerial and satellite imagery available on OSM is well out of date. The current drive is just the path labeled East Memorial Drive following the parking lots and exercise trail. The connection to Arnot Street is at the stop sign by the pool.

No. That's probably just a duplicate due to stale data, etc. I've merged them.

I think it's closer to department_store than to supermarket, since they don't sell groceries here, but I'm not an expert on the specific tags