To name a few, Jiho's ears turning red in the car is only visible in the webtoon (ch47) whereas in the novel, it's only speculated by Dani that he was embarrassed. They also added Jiho's POV when Dani called him in front of her class (ch69) which we never got in the novel. But they also took out some scenes, like a lot of Jiho and Dani's silly banter, which is a shame cuz they're hilarious but I get they have to condense things a little. In chapter 48 of the webtoon, Jiho says Dani's parents called him to bring everyone over to hang out with her. It's subtle but you can still kind of see how Dani's parents are more familiar with Jiho than the other guys. In the novel, it's more obvious cuz Dani says Jiho is the one who goes in and out of her house the most, to the point she derisively calls him the fourth resident of her house.
Ultimately, I think it's a bit of a wash as far as the subtlety of Jiho's feelings go in the webtoon (sometimes it's more obvious, sometimes it's toned down), but the novel is much better at showing how close Dani and Jiho actually are. It's more inferred here but the novel is quite upfront about it.
And yes, definitely. Jiho respects Dani's boundaries but he always makes an effort to be close with her. Dani more or less says she always kind of pushed Jiho away but he'd just throw a joke back at her in response and that gradually chipped away at the walls she put up till they became close friends. I feel like Chunyoung really shot himself in the foot by telling Dani he "liked" her because she didn't show any interest in him. It just made Dani put her heart under lock and key and stopped them from growing closer. This whole dichotomy/contrast between Jiho and Chunyoung stretches so many layers, like from the beginning of the story.
Do people really think Jiho's mean? I think he's a harmless troll and it adds another layer to him. He also teases Dani and jokes around with her so she'd feel more comfortable interacting with him that way. She even says despite all his sarcastic jokes, Jiho never does anything she actually hates.