What keys must be preserved when migrating an email server?

I'm setting up an email server and a web server on a VPS and in the near future I will probably need to wipe and reinstall the VPS. I used certbot to set up SSL and I've got a backup of /etc/letsencrypt so I can easily move that over to the new server. Do I need to preserve anything from the DKIM, DMARC, and SPF setups on this server or is it ok to generate it all again as long as I change the records with my domain registrar?

None of them "MUST" be preserved, but some or all can be.

For DKIM, you can make new keys and associated DNS records for the new server, or transfer the keys, or both.

For LE certs, you might want to keep copies "just in case" but when reinstalling, LE should authorize new certs and this is an easy way to be sure your server is configured correctly for when it comes time for automatic renewals.

DMARC and SPF are only DNS records for other servers. You may be using tools to evaluate mail received, but there are no keys associated, just configuration files.