Well, it's not easy to say off the top of my head. Different manga series might number their chapters differently for the Shibuya Arc. You could try searching on manga-specific websites or asking in manga communities for the accurate chapter.
Well, it's a bit hard to keep track precisely. Different sources might have different updates. But you can usually find the current arc mentioned on manga-related websites or social media groups dedicated to JJK.
It depends on how closely the movie followed the manga. But a good place to start might be the next major story arc or the chapter that directly follows the movie's ending. Check online manga guides for specific details.