1. Yes
2. Unit Slab, with ample leading, expanded 10% horizontally. There is a prejudice against horizontal scaling, but the effect varies from type to type, and IMO a face such as Unit Slab is not adversely affected by it; let your eyes be the judge.

Interesting. Thanks for that! You think several hundred pages of Unit Slab would be ok?

After looking at it in smaller samples I see what you mean. I haven't done any full books before and wouldn't have thought of anything but a "typical" serif.

You think several hundred pages of Unit Slab would be ok?

I don't know what kind of book you have in mind, or what kind of page layout.
I had assumed it would have a somewhat interesting design, being "a book that accompanies a magazine's branding".

Fair enough... I did imply that. :) It is a book that "shares" the magazine's branding, and true, it will have some unique layouts, but mostly it will be a standard "chapter book" type book.

Do you still think Unit would make a good choice? If not, any other thoughts/suggestions?

I don't see why not, but why not work with it on a page and see for yourself?
After all, if you are already using it in the magazine, wouldn't you want to see if such a magazine choice could also be made to work in the accompanying book? Isn't that the challenge, to find a typeface that has such brand consistency across two (or more) genres, and presumably different paper stock, and yet still excels in each?

While I would never blindly accept anyone's advice (even a guru such as yourself), I do see and agree with your point. "Try and see" is the only real way to find out. I tend to obsess over this kind of thing, so input is a good way to choose an investigative path, even if it is not the ultimate decision.

Thanks again for your input!