I can only advise 'Against' Manchester for a Stag Do!
I've lived here all my life, and it just isn't set up for Stag do's or large parties, it's an absolute pain to get in anywhere in large Male only groups, Most of the venues in the Northern Quarter you'd fill with your group size haha.
some cities are set up for stags (Liverpool, Newcastle, York), actively seeking punters, touts and promotions, Manchester just isn't like that from my experience.
Seen so many getting rejected from places over the years, so you'd have to play it cool, split up into smaller groups etc...
You'll be struggling for a decent club at the end of the night, unless there is a specific event on at Albert Hall or Gorilla, or Warehouse project (bit late for tickets on that front though), You've got Venus for Funky Vocal House, but limited capacity and very strict door policy.
Possibly best to stick around the student end of town and possibly certain bigger venues in the northern quarter.
Hotels, Ibis up in Ancoats not far from the northern quarter, best bet may be AirBnB or some of the serviced apartments as suggested.