I really need to start a csm FAQ for here.
Milling green is fine.
Only seal ends of the timber as fundamentally what happens when timber splits is the end grain dries out disproportionately faster than the rest of the piece. You seal ends to reduce moisture loss from the end grain, so hopefully dries even with rest off piece.
Sticker, have never been to concerned with what timber the stickers are made out of. Even been using chip board when it is available. Certain species may stain and require particular stickers, but not something I have experienced.
Make sure that your stickers line up, they should all be above each other with the slab in between. Depending on piece size, I like 1 sticker for each 2-3 feet of slab.