Coyle and Hall should compliment each other's games well. Think of Hall as a Marcus Johansson on steroids. That 3rd line played a big part in the Bruins' playoff success in 2019. There are question marks regarding what version of Coyle we will see, but I think Hall - Coyle - Smith could be a great line. Hall drives the play, can play pass and catch with Coyle, and can feed the puck to Smith. Where Hall is less physical, Coyle makes up for it for getting to the net and being great at possessing the pick along the boards and net. Smith will go on the forecheck and be the shooter on that line. On paper, that's not the most attractive looking 2nd line, but it should work in theory.
As for Studnicka, I don't think he is going to be given a spot on the roster. He's going to have to have one of the best training camps and outplay some of the veteran players for a spot. In my opinion, that should always be the case, but we know how Cassidy is. He will choose the vet who may not be playing so great over putting in the younger player.