...
That should be everything in SquaresDB to create the period. Don't forget to also update Historic Subscription Prices and Squares Pay with the new period, though.
Shortly before the period starts, you'll want to import the payments. The Squares Pay page has more on how to do that.
Debugging
Django sends error messages to squares-db-errorlog@mit.edu – if you're routinely debugging issues, you probably want to be on it.
...