Facing stainless is easy enough to do. The amount of material removed in each pass will depend on the size(rigidity, dampening mass) and horsepower of machine. Feed rates will depend on your machine and to a certain degree rpm. If you have vibration try increasing feed rate and decreasing rpm's. This will work as long as you aren't trying to remove huge amounts of material with a small mill. Start with a low depth of cut and increase feed rate and depth of cut until you get poor surface finish and excessive vibration.
To calculate rpm use this formula.
For carbide tools only use the value (500) Other materials, have different values. Stainless with High speed steel cutters would be 50 or 60. Aluminum would be around 100. Keep in mind the given rpm is conservative and only a reference. But its a good starting point.
500*4/diameter of cutter.