50 Ω impedance that requires smaller trace width (~4 to 6 mils). This needs more spacing between the traces (~3x). Spacing between non DDR signals and DDR signals must be ~4w to avoid crosstalk issues.
Address and control signals can be referenced to a power plane if a ground plane is not available. The power plane must be related to the memory interface. However, a ground reference is preferred. Address and control signals must be kept on a different routing layer from DQ, DQS, and DM to isolate crosstalk between the signals.