All very good questions -
There was talk when the finale for Season 6 aired that James Marsters wasn't aware of what was actually going to happen to Spike, so he played it like Spike was going to have the chip removed. I think he said he would've played it differently if he'd known Spike was going to get a soul. But I think Joss had said he didn't want James having any inside info b/c it would affect his performance.
So - it's possibly it could've done either way - and that Spike had gone to get his chip removed, but the demon gave him his soul to piss him off or something. Or Spike actually went to get his soul. There's still, I think, lots of fan debate over which it was and why.
About "Chosen" - I have no idea. The return of Spike's sould might have been part of a bigger picture, but that's what fanfic is for!
Let me come back when I'm a little more coherent and I might have some other thoughts.
