From the sound of the question, this is your first convertible top. If so, please fess up now.
The staples normally used in this job are ╝ wide, and 5/16 sounds like about the right length. The staplers I've always seen used were driven by a pneumatic stapler, because a lot of them get used doing the job right.
If you never did one I'd suggest paying somebody to watch how the job is done by a pro.