Is it surprising that Caliban willingly worships Stephano and desires to give him control of the island when he resents Prospero for usurping what he considers his rightful claim to the island? What does this show about Caliban?

No, it's not suprising. Caliban resents Prospero, therefore anything Stephano can do to change Prospero's position is a good and just action. Caliban believes Prospero to be the usurper; he hates the man....... and what it comes down to is that is it's not going to be him knocking Prospero off his high horse and ruling, it may as well be Stephano. Caliban is short sighted here..... the only thing he cares about is that Prospero be taken from the throne.