Any suggestions where a stag night could go in sheff. About 25-30 guys, bit worried bout getting in places

You've got no chance of getting in anywhere if you all arrive at once.
try staggering your entry in groups of 2-3.
I would recommend Spearmint Rhino for a stag night, mint birds, and the drinks are about the same price as anywhere upmarket(ish) in Sheffield. Then after that, your only a few steps from the Leadmill, which is always a good laugh.