The people who complain about Kazuya clearly have never dealt with anxiety issues. It's clear as day that he suffers from it and the constant overthinking is apart of it. Makes him seem somewhat realer to me. He has no idea how the person that he loves feels about him. He also has to balance that with being delicate because she is going through a tough time. Thats not easy to deal with.
I think he's been nothing short of a good guy throughout all of this since the movie arc started. The maturity he has shown is being ignored due to him freaking out is used as comic relief.
Re: Chizuru, she knows full well that Kazuya is not just "a client". She needs to figure out what she really feels for him. Either way, the true feelings will come out for better or worse.