For example, the absolute maximum they pay anyone in SF is 160k.

What "grade" would candidates for "Software Developer" have? What determines the "step" ?

As I recall, they tend to start the senior folks at grade 15. They have to get approval for starting at any step above step 1, and I don't know how often that approval is granted.

They are very open about all this during the process.

That's right. There's no set grade or step for engineers, but most of our senior engineers start at a 15. Your grade and step (and therefore your pay) are determined by previous experience and previous pay.

that sounds bad, different location different pay

But note that they can make exceptions to the pay scale (at least, move you around under the overall cap).

When you change locations, your pay rate is also changed, correct?

Correct.

What's the working level grade for engineers?

There isn't a set grade level for engineers, but most of our staff starts at a GS 14 or 15.

What about for entry-level candidates?