Hi Don,
From network perspective, you just need to ensure 2 things:
1. The DR site is reachable from all the remote sites (for DR purposes) including the current production center(for replication)
2. The path to the current production center is primary and the one to DR site is secondary in all remote locations.
However, to check complete readiness, you can try using a separate test subnet at the production and DR site so that once you disconnect that subnet at production site, traffic shud flow towards the DR site.