Alumide probably wouldn't work as a molding material, as it is weaker that WSF, but has the same grainy texture. I don't know how well stainless steel would work for making molds, but silicon rubber would work fine. It would probably be best to print masters in frosted detail or frosted ultra detail. However, casting takes a lot of work, and generally it is hard to produce as good results as just printing the entire puzzle, which is why casting is not widely used for making puzzles anymore. As for sticker cutters, I recently bought a USCutter MH365
(the 14" cutter on the list), and it seems to be the best deal I could find. I've already cut stickers for several puzzles with it, and I haven't run into any issues with the cutter yet.
Only on this forum would people use a V-cube 7 as a size comparison for a cat
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