When you Import an Illustrator file, it is brought into Strata as a Shape. You may extrude the entire Shape in the main modeling window.
At this point, if the Shape contains multiple paths, it is converted to a Group. If you open this Group into its own window, you will be able to access the individual paths. This will allow you to edit the bevel.
Open the Group by double-clicking it. Select all objects within the Group. As long as all objects are selected as you edit the bevel, the same bevel will apply to all objects.
Alternately, you could directly Open the Illustrator file rather than Importing it, to avoid the initial creation of a Shape. This allows you to immediately access the individual paths directly in the main modeling window.