Only data pointers. void * can hold any data pointer, but not function pointers.
Here is a C FAQ.
void *’s are only guaranteed to hold object (i.e. data) pointers; it
is not portable to convert a function pointer to type void *. (On some
machines, function addresses can be very large, bigger than any data
pointers.)
As for the first part, yes, different types can have pointers of different sizes: