I'd top mount your poster/stickers on black mat. Non-asid free 32" x 40" costs me $3. If you need oversized, 40" x 60" they run $8. You'll need some dry mount spray, I think Home Depot carries 3M #72. Don't use any number higher than #72 or it will be to hard to handle. You can use hot glue or clear silicone to mount the keys. Clear glass for 32" x 40" runs about $9 and 40" x 60" cost about $20. Plexiglass is much lighter, but will cost about 4 times as much. Good Luck