yes But through other relays if i am not mistaken

If you want to make sure to not Get censored and keep a copy of your notes i think you guarantee it with your own relay

But i am not so technical so cant say for sure

No. Relays can whitelist or blacklist anyone so the only sure fire way is to broadcast to your own metal. Anything else is just hoping someone else has enough interest in your content to keep it alive on their servers.