I only pinned (for the most part) in the seam allowance, and then my blocks went in folders with plastic pockets in them. I think if you use good quality pins, and keep them in a dry atmosphere, they should be OK. I had considered staples, but I thought they would be much more likely to rust.
I doubt if the glue on the back of a label would harm your block that much, but on the other hand, I doubt if they would stay in place for any length of time. I have visions of them curling up and coming off if you handle them too much.
Have you checked ebay for the rulers Athena? There are some on there for $11.95 - I don't know how that compares with elsewhere, I got mine with the software, so I don't know what they cost on their own.