5"w x 2"h is about what we use to create them for colleges that present b-balls to players for breaking records. You can have a few lines within that and it's not much fun doing them.
We use our finger to apply and take our time... no money in them for us for sure. But it's one of the those products that they like order. The curvature of the ball with transfer tape makes it slightly tricky. But the reduced size for the length makes it bearable. I have never seen a template I would suggest to trust your eyes and do a couple test sizes. They take up no space even on a 24" roll, so do multiple sizes and select the one that best works for you based on the content.