What objects have the same memory location (eq? each other)?
As far as I understand one location can only have one object.
What order are internal definitions evaluated in, especially with regards to mutually recursive internal definitions?
If you need a defined order of evaluation, you can use letrec*. Do you have any examples where this actually matters for mutually recursive definitions? I can't think of any.
How large is the numeric tower?
It has five levels, from top to bottom: number, complex, real, rational and integer.
What compound data structures have copy-on-write versus mutable implementations?
None of the standard ones have copy-on-write.
Can the way continuations are implemented make programs slower, even if they are used appropriately?
Yes, there are no performance guarantees in the standard.
How do you call foreign functions in Scheme?
There's no standard way to do it.