There is no limit except to what your computer (and patience) can
handle... The most time-consuming and computer intensive tasks are
generating the possible outcome reports when there are 16 teams left in
To test whether OfficePool will be able to handle your pool, you can just create as many brackets as you think you will have, either manually or you can use the QuikPik feature (Brackets -> Generate QuikPiks... menu item).
Once you have the number of brackets you would like to test, then fill "The Results" bracket through the first two rounds (Brackets -> Pick Favorites -> Sweet 16 menu item) and then go to the reports section. This will then generate the Possible Outcomes report and give you an idea of whether OfficePool will work for you or not.
If Possible Outcomes is not important to you then you can turn this off and that will speed up generation of reports. Make sure "Prompt before calculating Possible Outcomes" preference (Preferences menu item, Reports tab) is selected so that you will be asked whether you want to run them or not.