I have to wonder how this ties in to Dementors, who can suck the soul out of someone's body.

Can the Dementors return the bit of Voldemort-soul to him if they take it from Harry?

One possibility for Godric's Hollow is that Voldemort just didn't realize what would happen if he put all of his soul into Horcruci - after all, no one has ever made more than one before. He overdid it, and ended up dead.

To become rebodied, he had to take something from Nagini in the unicorn-blood and snake-venom potion; part of his soul, maybe?

Just throwing things out there.