Weston at Dublin is the place to pop into for a day out in Dublin. Then onto Sligo which is GA friendly out on the west coast. From there you can do the Father Ted Island which is Inismoor. There are three islands in the group (Arran Islands) all of which have an airfield. Wish I was going with you!
Without looking I would say your shortest crossing would be to head out to Castle Kennedy and across to Newtownards. I'm a bit further south so my crossing is Anglesey direct to Dublin.