Yes, you can revoke the key and publish the revocation. This means that it will be flagged as revoked in the server keys and assuming that senders keep their GPG keybase up to date with server keys, they'll get a warning that this key is out of date. All e-mails already encrypted with the key can still be decrypted though.
As for the second part of your post, you're probably asking about this:
As for the second part of your post, you're probably asking about this:
https://alexcabal.com/creating-the-perfect-gpg-keypair/