Should my S3 bucket for Storage Studio be public?
Short answer: No. Keep Block Public Access fully on. Storage Studio uses your access key, so the bucket never needs to be public. Amazon's default encryption setting is the right choice too.
No. Leave Block Public Access fully on. Storage Studio signs in with your access key, so the bucket never needs to be public, and backups especially should never be readable by anyone else.
When creating the bucket, Amazon's default encryption option is the right choice too. Pick the region closest to you and write it down — you'll need it for the Region field.