I was just going to suggest that you have a limit on the size of the paper so that you won't have a 400 foot scroll come in. Call it something like anything that could reasonably scanned. That would be the standard I'd recommend. If you can reasonably scan it, it's fine. I don't care if it's A4 or letter size. If you can scan it, it's fine.
Personally, I don't have a problem with postcards being accepted. I don't know what my colleagues think. We get a lot of postcards, why can't they be counted as petitions? If you get 25 postcards with the same message and same signature, what difference does it make if it's one or ten on a page. That's my thought on that.