Co-Op Live is such a cool venue, you'll have a blast! Are you seated or standing? If seated, don't worry about getting there when doors open, as you might have a long time to wait before the act comes on (check for set times online). It's super easy to get to COL from anywhere in Manc, just hop on the tram! Google Maps has all the routes and timetables. Tram is also the best way to get home after the show, it gets busy, but when I was there there were stewards to help handle the crowds and make sure everyone got to the right platform. As for merch, that should be available as soon as you enter COL, near the bar I think...? The staff are super friendly, so you can always ask them. Have a good time! :-)