The tip of my SM57 seems to twist left to right like a screw cap but doesn't actually come off, si this normal?
Yep, they do that.

I'm not quite sure what the function of it is though. You ask certain members of the studio staff a question and get a different answer...
Yep, they all do that, I had the same problem when I bought my first one ages ago, I took it back to the shop and the dudes laughed at me. haha
I'm the new king
I taste the queen
In here we are all anemic
In here, anemic and sweet
Me too....

Could I get some more talent in the monitors, please?

I know it sounds crazy, but try to learn to inhale your voice. www.thebelcantotechnique.com

Chris is the king of relating music things to other objects in real life.