90deg angles are implied for 90deg angles. You do not need to add 90deg dimensions unless there is some ambiguity (exteremly rare). Standard tolerance for angles that is stated on your drawing still applies, so be careful.
Centerlines do not imply anything other than they are going through the center of something. They do not provide you with any dimensions or tolerances. If you do not dimension to them, they pretty much mean nothing, not even symmetry. Just about the only thing you can assume in your example is that they are 90deg to the Line B.