How to organize email recipients in professional group email?
It doesn't matter.

Certainly, in Sweden it doesn't matter.

Nor does it matter anywhere else.

The only things you might want to consider:


To: or Cc: header: some e-mail clients show e-mail differently if the recipient is in the To:-header as opposed to the Cc:-header.  Gmail is one such client.  I tend to prioritise e-mails where I'm in the To:-header over those where I'm in the Cc:-header.  If you expect the professor to answer your question, make sure he or she is in the To:-header.  If you just wish to “keep him/her in the loop” (perhaps for future reference), Cc: is fine.
Avoid bcc, as most e-mail clients and servers ignore the rule that the recipient in the bcc should still see their own name there (but no-one else should), and therefore it will look like an e-mail not addressed to them at all.  That makes it downprioritised at best, or marked as spam at worst.


But really.  Within that, nobody cares about the order of the recipients.