Suspending sales first means there won't be any ticket buyers that slip through the cracks and buy tickets to an event you have officially cancelled.
Letting your patrons know about the cancellation via mass email before refunding or converting the tickets will ensure they don't reach out in confusion about why their order was cancelled without their consent.
Make sure to convert your tickets to donations or refund them before the show closes out. If you fail to do so, all refunds will need to be processed out of your organization's portion of the settlement check.