She killed Urasue as a kind of laugh in the face. Urasue thought that when she brought Kikyō back from the dead, Kikyō would do whatever she wanted. So as her first act, Kikyō killed Urasue just to spite her.
As for her finding the perks to her new body... Her undead clay body did not need food or water and was very durable. She fell off three different cliffs in the series and survived every time! What's not convenient about that?
But for the most part, Kikyō was very unhappy with her clay body. It wasn't a living thing and she had to use human souls to keep it working; it did not age or change; and it was always cold because it was just clay (there were many times when Kikyō envied Kagome for having bodily warmth, because it meant she was alive). The thing she hated most about her body was that even though she wasn't technically dead anymore and she had a body that existed in the world of the living, it didn't mean she was alive. She would never have a place in the world because she wasn't a living thing. That was the main reason she was angry after she came back. Even though she cheated death in a way, she still didn't beat it.