See Travel section for best time to book flights and other info on how to get to Belfast!
Again, see Travel section for details regarding this question! Jack and Katie's preferred route is the bus that goes direct to Belfast from Dublin Airport.
Katie and Jack will be staying at the Merchant Hotel. That being said, all three hotel options are walking distance and all activities before the wedding will be in Belfast City Center.
Yes, Semi-Formal to Formal attire is encouraged. This means either cocktail dresses or floor length dresses for the girls, and a suit and tie for the men.