First- Is it your intention to abandon Lightroom-Classic altogether?
Do you intend to work only with the Lightroom apps? (Lightroom-Desktop, Lightroom-Mobile, Lightroom-Web.)
Do you have enough Cloud storage that Lr requires to store 68,000 photo files? (What is your plan?- 20GB or 1TB?)
Are you willing to spend the time uploading those full-size files to the Cloud?
Do not break your Lightroom-Classic catalog into smaller catalogs- that is a backward step not generally recommended. Your LrC catalog is not large.
Lastly- if you do intend to abandon Lightroom-Classic then the ‘Migrate’ command is in Lightroom-Desktop (Not Lightroom-Classic).
Personally I find that maintaining LrC as my prime editor, and syncing selected photos from Collections is a workflow that suits me, and I use only very minimal space in my cloud storage. (Syncs from LrC up to Lr do not use any space in Cloud.!). And phone photos automatically download to my LrC catalog with edits syncing LrC<>Lr..