Actually, you'll probably fly to London. I don't know. Check prices to Belfast, as well. Then you could visit Monkey. By then, the ferry to Campelltown should be running again. Belfast, two nights. Ferry to Scotland, toot along via Glasgow, maybe a Wall thing, then hit Edinburgh.
If London, a couple nights there ($$$) and then grab the new wobbly train to Newcastle. That train ride is cool. It moves on the wheels, so you don't feel anything. Like a spaceship!
Hit Newcastle, do the brewery thing, take the little bitty goober train to Brampton. Start on the Brampton hiking trail (the TIC will give you directions) through woods and pasture to the start of the truly dramatic parts of the Wall. Walk and camp in either direction, then just drop back down to any town and hit the train back to Newcastle and then north to the fest.
Also remember-- going east is worse for jetlag. Try to fly a day flight, landing at night, and you'll thank me in the morning.
And, with two weeks, and a solidly planned stop in Scotland, don't worry about the Euro. You'll be trapped if you want to take your time, camp and enjoy stuff. Dont't try to take in 50 countries in two days, your vacation will suck. You could spend two fucking weeks just on Hadrian's Wall. The country is full of so much... But note that the pound is almost two for one, now. Budget accordingly. A thousand dollar vacation will be a 500 vacation. Your daily outgo, on the Pound, will be about 50 bucks per person. Maybe more.
Which is why I stress the importance of the plane ticket. Everyone's like you. Poo-poo-poo, $450 is on Death Airlines. I should pay a million dollars for United, AKA Death Airlines. Wrong. They're all competing, they'll cheap as dirt. Just be patient and observant.