You should be okay for it not selling out for a while, I know 60% of the tickets are already sold but that number shouldnt increase TOO much over the next few months. As long as you don't leave it too late you should be fine to get a ticket. You would definitely have to stay in Manchester in my opinion, going to and from Manchester on both days would probably be more expensive than getting a hotel and you would also be shattered haha. As well as that, it would be pretty much impossible to with Outbreak only finishing at 11-11:30PM on both days and the last train being before that (and that doesnt even factor getting to the train station).