max characters in a var is around 941 but it reduces the longer your var name is, 941 is for a /set %x which means its got 8 charactes in front of the text, so its like any line maxes out at 949 to 950 characters.

number of vars allowed i beleive is unlimited, HOWEVER the script editor truncs the list at 64k i beleive and well loose any after that if u alter any in it. If u dont look in the vars section of the editor its unlimited (i think)