Consider cleaning out old patron files;
Fines that you do not want to bring over should be forgiven;
You also may need to clean up any coding errors that may prevent items from being mapped to locations;
Consider control field coding that needs to be cleaned up.
Local tags may need to be reviewed (how you are marking them). Alma Migration Considerations for Consortia - Ex Libris Knowledge Center (exlibrisgroup.com)
If there are any carts of weeded items to be purged, it would be useful to get that done prior to cutover.
Manage space
Manage content
Integrations