MAPI-over-HTTP using Exchange-iApp (order of iRules)

Yes, the default in the switch will be triggered.

If you want 2 iRules, you need the IMAP one before the combined iRule. You could also include the IMAP in the combined iRule.

Both have the same effect.

There is no right or wrong in this case. Just that a single iRule will be more efficient, as there is only one switch.