A:AnswerYes. It will partly block the vent you connect it too. But you can play around with it some. I had to position mine so the the air did not blow too much on the passenger, per their request.
It is great for hands-free phone use.
A:AnswerI don’t know about the pixel 3 specifically but I do have to remove the case for it to work with my V30 so I assume it would also need the case removed for other phones.
A:AnswerYes, it extends out from the sides and from the bottom, and both are adjustable. The arms open with a button on the lower right side but you have to manually close them. I have a note 8 and my phone fits just fine.