[IBMiOSS] Understanding SSH Key Pairs

Hi All

I'm required to switch from FTP to sFTP, and first that means negotiating
OpenSSH. I want to really understand this, because I don't think the person
on the server side does and I think one of us should.

I've read a couple of tutorials, but I'm stuck on the concept of public and
private keys.

In the context of an IBM i being the client (me), and a non-IBM i being the
server (my client's customer):

Do both parties generate both private and public keys?
Which party gives his public key to the other? (or do both, or only one,
but it doesn't matter which?)
How many keys are there in total? e.g. Do both parties share the same
public key, with each having his own private key?
If you generate your private key from the public, what stops a baddy from
intercepting your public key and doing the same generation then
impersonating you?
Do you get a different private key each time you generate from the public
key? Would this then be invalid for a connection you've used before? e.g.
If you test with one User Profile then switch to another.

As you can see from these questions, I'm really devoid of basic
understanding of how this concept is supposed to work. Feel free to answer
the above questions point by point, or to explain via a short summary or a
metaphor/analogy if that's easier.

Thanks.