No Order Number = Nothing From Support?

No, because that requires an out-of-band secure communication method for bootstrapping the secret, in which case you may as well use that for your entire support ticket instead.

No, the order number is required in the email subject for technical support, but PGP encryption is optional.

Probably not, considering the amount of emails they get:

Possibly:

No, the Purism support team has reduced capacity at the moment: