If you run out of space, then yes, the query fails. You don't have to restrict sizes, though as Jason mentioned, this is recommended in some cases. Not sure how many. Ultimately, there is a restriction: the size of the drive.

I would size these high, make them the same size, and make sure all autogrow settings are the same.

If you grow them manually (monitor to see your % of use over time), grow all files by the same amount at the same time.