As a current physiotherapy studenf going into my 3rd year at Calley, I can give you a decent idea of what you're getting yourself into at GCU.
Sounds like most of you have picked degrees that are part of the School of Health and Social Care, and to be completely honest this is probably the most highly-touted of the university's departments gaining high recognition throughout the UK for their teaching style and overall end product in terms of student success.
Anyways... enough of the business side of things, being in the city centre is great and even if you wanted to be part of the west end scene or catch up with people in the west end you're either a 15/20 minutes walk or 5 minute subway/taxi from hillhead station and ashton lane/byres road.
As one of you mentioned already, it's a very easy to navigate, compact campus but doesn't have a Union as such on it's own campus. For the last two years that I've been at the university Walkabout next to the Cineworld in the city centre has been our"union" and have had a deal with them to get better drink promos especially on Wednesday nights after the sports teams have played and everyone's coming back into town for a night out.
As for accomodation, my first year I actually stayed at Victoria Halls just another block or so up the hill from calley court. Depending on what you're looking for this is another really good option for at least the first year of Uni.
If you want to know anything else here, let me know... feel free to get in touch with me by private message as well if you have any specific questions or concerns.
Good Luck, and Enjoy!