The answers to the first two questions readily follow from Proposition 7.5.2 in [J. C. McConnelMcConnell and J. C. Robson, "Noncommutative Noetherian rings", AMS, 1987]. Actually, they prove a much more general result which holds for skew polynomial rings and skew Laurent polynomial rings. The base ring $R$ can be arbitrary, not necessarily commutative.