Permanent Adhesive? can I foil stamp on these? Can I get solid sheets 8.5 x 11? Thanks!

The Clear Gloss for Laser does have a permanent adhesive and is available on our full sheets as well. I have included a link below to our full sheet label options as well as a link to our free sample request page. Since we have not tested this material with foil stamping, I would recommend requesting samples first. https://www.onlinelabels.com/full-sheet-labels.htm https://www.onlinelabels.com/samples

is the reverse (adhesive) side of the label silver or white?

The adhesive side of our Weatherproof Silver Polyester Laser (SP) is silver. If you'd like to receive samples to take a closer look at the material and test with your application, please feel free to visit the link below. https://www.onlinelabels.com/samples

DO these come in packages of 20, 25, 50 sheets, or do I order the specific number of sheets that I need ?

OL159WG is a standard item so you can order any specific quantity of sheets. Just above the 10 sheet option on the product page, you can specify the sheet quantity needed in the field below "How many sheets do you need?"