Okay so just made the trip back to the dark side after a decade away.  I bought a G23 a couple months ago and even though I haven't had much range time, I'm hooked again.  

First question is I'm just finding out about the SF and I think that might be just what I need. Im planning on selling a rather nice 1911 and replacing it with 3 glocks.

How can I tell if the G23 that I have now is a SF?  My big reason for getting out of glocks and carrying the 1911 was the fact my hand fit the 1911 better but this might change everything ?

My thought was to buy a full size g21 the compact 9mm I forget the number and then replace my back up gun with either the sub compact 9 or 45. Open to thoughts.

Sorry if any of this sounds dumb, as I said I've been out of the glock world of a bit.

Never mind about the sf question it appears it should be stamped on the side

I don't think a glock 23 SF exists.

The SF option is only available on the 45/10mm models (20, 21, 29, 30)

There is no G23 SF model.  It already has the standard small frame that the 9mm/.40/.357's use.  The SF model is offered in the 20, 21, 29 and 30 (.45 and 10mm) only to the best of my knowledge.  You can tell an SF model by looking at the right side of the frame forward of the trigger guard, where you'll see an "SF" in the frame.