This is something I want to know. Lets say Vaporeon (base 130 HP) used Wish and then switched out to Shuckle. Would Shuckle's HP be restored, and if yes, would it be restored by half is max or by more (because Shuckle's max HP is lower)?

seconding everything pinsir said, but I'm not sure what "always does" means. wish will always heal half of the wish users hp. meaning that if you have a vaporeon with max 130 hp and switch to shuckle, the shuckle will get 65 hp restored.

Yes, shuckle will be healed as long as it has some damage. If shuckle is fully healed(in hp) then wish will fail. Also, if you use wish then your Pokemon faints, then wish won't activate. Also, wish will heal the same amount of hp as it always does. Hope this helps!