Hi.
I do not know if there is a limit, but i do know that you should avoid using globals.
i did the same before, but now i usually have only 1 or 2 maximum in a project.
I mostly use get/set sfm action and the are more actions on the ecosystem like fsm add int, fsm bool test, etc.
if i have a variable that needs to be accessible by many objects, then i set a empty object with an fsm (i call it meta) and on play i set that one into a global for easier access.
Have a look at this wiki page :
https://hutonggames.fogbugz.com/default.asp?W1462