Depends on your mechanical requirements. The core thickness will make a small difference in your 50ohm trace widths, which will be close to 0.12mm with 0.1mm prepreg thickness.
The via stub lengths only start to make a difference past 3GHz, so it's a non-concern for DDR3.
Of far greater concern is the planes stitching. Every time your DDR trace changes layers, ground currents have nowhere to flow and must go to the nearest stitching via. If you used power planes, every stitching point requires a capacitor. You need a capacitor at least every 5mm or so (depending on DDR speed). For speeds >= 1866Mb/s I recommend using only ground planes, and putting a ground stitching via next to every signal via.