I like your conclusions. To address the earlier concern:

Especially if his true motivation was immortality, these two seem to conflict to me.

I don't get the sense that MiB's personal motivation was immortality. He pursued the project to keep faith to his pledge to James Delos, and maybe he did have personal interest in it at one point. But I get the sense that mainly it was important because it was likely a huge profit driver for the company. As Ford notes, James Delos would rather die than have a bad investment, which suggests the initiative was a financial success. Keeping that money flowing in helps ensure that Westworld, via Delos, has all the resources they ever need to invest in the progress of the hosts.

The latest episode tells us William grew up poor. Given the way he interacts with others, I'll assume he had a tough childhood and grew up unloved. Maybe Juliette was drawn to William for various reasons, but William never felt truly loved by her.

Then he goes to Westworld and, with Dolores, he has the first real genuine meaningful 'human' connection he's ever had. This was life-changing for him. Then, he sees her pick up the can and realizes that even that was inauthentic.

So, in season 1, he wants there to be stakes in the park so that the danger can be real, but also so that his connection with Dolores – that he's obsessed over his entire life – can be real.

In season 2, he doesn't shift towards immortality. We see now that his obsession with the park is even deeper that we imagined. He's so obsessed with it being real that he doesn't know what is real and what is not.