Yeah.
That's right. Upgrading won't erase your certificates or configuration, and everything should keep working as before.
Yes. The Certbot package includes a systemd timer and cron job. (The latter will disable itself since you're using systemd.)
If your current cron job includes other options (like a hook to reload a mail server) you'll have to do something about configuring that, though.
For what it's worth, the Certbot package keeps /usr/bin/letsencrypt. (Replacing it with a symlink to /usr/bin/certbot.) So you can start running "certbot", but your old "letsencrypt" workflow won't stop working.
You can run "certbot renew --dry-run" to test renewing still works.