We often use polystyrene for the same purpose - you have to run the toolpath in reverse which leaves the burrs on the letter and the edges of the stencil clean.
I think this is called climb milling - its a toggle in my program.
Oh - a hint - if you have scrap vinyl on hand apply a layer to your sheet before routing - the flexible quality of the intermediate vinyl really extends the life of these stencils.
Another hint - use your router to cut your sanblast resist. Apply the resist to your substrate, then use a 15 degree cutter to cut the resist. This prevents the resist from stretching when transfering it from the carrier sheet - in general making the whole process easier. We also pre-prime the substrate to give the resist a better grab surface which means we can use less aggresive resists.
GL.
Worry about success, failure takes care of itself.