Sounds like you'll be working with us for awhile.
Cyrus will charter a naval transport between here and Stormwind, but I expect you'll want something a bit faster for day to day use.
Head back upstairs and take a left when you get outside. You'll find an old study where the Tidesages used to conduct their magic rituals.
Surely your Alliance mages have already sensed its power.
Inform them they may open their portals there. The harbor guards will keep the room secure.