I'm holding my judgement for a couple more chapters. I don't really think a truly faithful adaptation of the LN would make a very good manga so it really depends on what these changes are in service of.
Pretty much as a rule, I always end up feeling bad for the love rival characters, even if they're obviously shitty people, but Kokoro is really testing that. :angery:
If I had to guess, Kurumi won't back down about breaking up with Kokoro but Naoi will be more tepid about her relationship with Kudou, as sort of a reverse parallel to the situation in the first two volumes.
My speculation would be that Masaki doesn't know Michi personally, but did know of Michi through Aizawa, and her connection to Aizawa is why Masaki is interested in her.