stac info /path/to/catalog.json
seems like a natural utility to add to that. Are you going to be at the STAC sprint, and want to touch base around potentially combining efforts on that?
sentinel-s2-l2a-cogs
collection is what you want. sentinel-s2-l1c
and sentinel-s2-l2a
are catalogs for the original JP2K files in eu-central-1 and are in requester pays buckets. But the COGs are free