A #320 grit stone is perfect for knives that haven't seen a whetstone for a while. It will help you achieve a new edge on your knife very quickly but will need refining on finer grit stones as the edge left after a #320 grit stone will feel almost serrated and rough.
Suehiro's Cerax line of stones are one of the most reputable synthetic stones available. They have wonderful feed back, Develop a beautiful slurry, cut fast, stay flat a long time and require no soaking and they're effective with any type of steel; what more can we say. We use the Cerax line to sharpen all the knives that come into the shop to be sharpened and we love them. Each stone includes a rubber stand that will keep the stone from sliding around on what ever surface you're working on and a Nagura stone (dressing stone) which will help pull steel out of the stone as it gets clogged up.