I have worked with Data Migration and Integration heavily with CRM. I would need some time to get the details around the conditions lined up for how to determine what needs to be merged. I would be able to work through the logic. If possible, I would prefer if I could obtain access to an environment to test in. If a testing environment is not provided, it would be helpful to know whether you are able to forward me a copy of the database or at least the contact table.
This will be imperative to ensuring that there is no flawed logic on the merges and that the action completes successfully. The first question I have is how many contacts are you looking to merge? How quickly does the operation need to run (over one night or a weekend?) or is this something that can be done during business hours? If you intend on running it during business hours, there may be a negative impact to the performance of the environment depending on the size of the contact table and if you have an extensive amount of plug-ins that fire on contact update.
I have done operations like these in the past and I am the right fit for this merge. Please let me know if you need additional details from me. Otherwise, I look forward to hearing back from you, have a great day.