The real problem is you're trying to assign keys before you've even determined the needed entities and their attributes! [/i] That's the big problem with the false notion that identity should be a "default" key: there should be NO such thing. Each PK and alternate key should be carefully chosen based specifically on the data itself.
Of course you are right and I'm sure you understand these concepts inside and out. But the OP sounded to me like a complete beginner and your rigorous analysis may be quite beyond him in this early stage of his explorations. I just suggested one quick way he might get up and running.
Knowing how much help to offer is always a sticky question, isnt' it?
BTW, at no time did I tell say that people should always use identity fields as 'default' keys. False notion or not, I didn't say that.
Sigerson
"No pressure, no diamonds." - Thomas Carlyle