No more than 3 at any one time and even that depends on whether the pilot is known to be experienced or not and/or has a good command of English.
I would never give a pressure setting and a squawk at the same time and would strongly advise any trainee atco not to either.
A colleague recently gave a very experienced pilot the surface wind, QNH and squawk all in one transmission - the pilot got airborne squaking the surface wind.....
Nuff said...
