Same here. At first, I was confused because game 9 expands upon Yuki's motives and goals, but then I realized they probably want to extend her mysterious image as it suits the atmosphere they're going for. They're likely going to drop her background and history in smaller chunks.
Yes! So far (episode 4), they have made some adjustments (timeline, small details) and additions (mostly fleshing out other character's backgrounds and adding scenes that really show how televised these games are), but all of the changes have been very complementary.
The manga follows the novels more closely arc-wise (game 9 before game 10, while the anime shows game 10 first), though both the manga and anime hae taken liberties with adding additional depth and details onto the original story. The writing style of the novels is blunt and to the point, which...