Hey @MKnoesen
si I’d divide the problem into 2 different steps
1) De duplication of the contacts: I’d start by deduplicating and merging contact in 1 portal. Once you have all your data clean, then go to step 2.
2) Move contacts from portal A to portal B: Here you can use 3rd party apps like HubSpot to HubSpot Migrator or Portal Replicator to copy the information (contacts, companies, deals) from one portal to another. This may have an extra cost but if you are dealing with a big amount of info, will definitely help you.
At this pount you can always opt to export you contacts/company/deals/tickes into an excel/csv from portal 1 and import manually into portal 2.
If the most importan information is in portal 1, I wll erase fists all the contacts from portal 2 to avoid having duplicates agains, and have a fresh start.
Hope this helps