I suppose it should be possible to open a corpse for enchantment and instill effects that animate it under an enchanters control?
Charm against putrefactin, awaken the slumbering corpse and the like.
I don't see why not. It'd be a huge thing made of bone (well, that's the highest level component), so 5 x 3 =15 vis to open / worth of effects.
A heck of a creepy talisman.
Don't see why not. But is it considered an item of shoddy quality? 
City & Guild p. 70 box
Yes, you can. Hermetic Projects is pretty clear on allowing this. However, HP also warns you against enchanting the entire corpse because it's pretty easy to damage a corpse, suggesting instead that you might choose to stick the magic in something sturdier. Even the skull is much less likely to be destroyed than the body as a whole. You should really read through that section of HP if you want to do this.
I had a fun character who found a ghost of a recently dead person, preserved the corpse, bound the ghost as a familiar, enchanted the skull as part of the body as his talisman, and then attached his familiar to his talisman. He also had Quiet Magic x2 and Subtle Magic. They would pretend as though the familiar was casting the spells since his talisman extended his touch, so he just had to be touching his familiar's body. It was cool. And no one figured it out. That saga died before we got really far, though.
Yes! In fact there's an example of just such a device in the Covenants book.
Yeah, most people are indeed shoddy craftmanship, made by unskilled workers.
But we ignore that unfortunate D&D-ism. It should never have made it into print.