Set Outlook as my default mail system

Not that I'm aware of. I had to go through the steps of setting up my account in Mail just for the purpose of being able to get at Mail's preferences to tell it to make Outlook the default email app. Then I removed the account I had just made in Mail.

It is a nuisance, but as long as you make sure to set up the Mail account as IMAP/SMTP, the same mail will still be there under Outlook and not offloaded from the mail server to your Mac as POP would do.