Hi Judith,
Approximately how many tasks are there per client? Are "Sys 1", "Sys 2" clients or systems? How long do you anticipate one migration to take? How long for all 1200 clients? Does the same consultant handle multiple migrations? Can the same consultant do several migrations at a time or do you need to stagger starts?

Initially I would create a template listing all common tasks for the migration. Depending upon how many tasks per migration, you might consider creating a project file for each client and then consolidating the multiple files onto a master project. As new clients are added, you just add the new project to the master. As client projects are finished - they are removed from the master.

You could use spare fields to keep further identification per client if needed. Regarding emailing status updates, create the view you need and send a PDF file.

Hard to give much more concrete advice without some questions answered - but feel free to continue the conversation here.

Best,
Julie