Casting decisions are taken jointly by the channel and the producers. Mishal was first approached by Playtime and the channel too liked him as Dutta after he gave a test shot.
Look as in outfits were done by the creative team with help from designers. The look and the mannerisms usually are thought about by the people etching out the character. However, the "outfits" could undergo some change from the original imagination in order to make him/her look "distinct" from the rest of the characters on TV. So I think again, it's a team effort. Dutta's overall look was inputs from a lot of people including the designers who suggested the outfits β the loose watch is a very integral part of Mishal's own personality and it seemed to go well on the character too, so it was retained. However, the kind of watches Dutta would wear was decided by the creative team, so it was more golden strap. The ring he wore on his right hand was also a very 'Maharashtrian' inclusion. The earrings came about as an element of quirk but actually Maharashtrian Brahmin men do pierce their ear β usually the left and usually wear two "baalis". So it was a bit of both. Mishal was very aware about his character and so he also groomed himself to fit the role. His contributions - i think he did give his inputs on the hair styling and also the rolling up of the sleeves of his outfit.
Mannerisms of course were taken from various living and fictitious characters. A lot of it was real - like his habit of circling the tip of his thumb over his finger while he is thinking; pressing his palm with his finger when he is trying to find his words; his pauses and his thoughts were all intrinsic traits. What else about mannerisms?
What is closet Dutta Patil? π I don't know about that, but yes, he would never wear the earrings or that golden strap flat watch for real π π I don't think he would even dress like Dutta for real. I think he has said that himself too. I don't think he has an arms license at all forget having guns π so ya... but I feel he did take it up because it was unlike him and it is very easy to play someone who is like you β but it is more challenging to be someone with too many layers. The two evident similarities could be that he doesn't hold unnecessary grudges with people and he is sensitive like Dutta.