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Hey Mike, I would publish content right away on the new site. You can also share in social to help get more inbound links and shares to the new site. Thanks! John

What are the risks involved? Lose Traffic and Rank you will found much information out there about that. In my own experience, you will have a drop in traffic that you will recover in time-frame 3-6 months. No matter how well you made the migration What are the risks involved? In your case, I would be building links to your site even before running the migration also creating social signals in order to avoid the Google sand box