A vinyl pool has no calcium need. It is generally stated here that a level between 0 - 500 is acceptible for a vinyl pool.
If you have a heater, you do need calcium. I saw a recommendation from Ben that said 60ppm is probably enough.
By "salt water system" do you mean that you want to add salt to your pool, or that you are going to purchase a salt water chlorine generator (SWG)? I do not think calcium has any bearing on a SWG, but I could be wrong about that. If you are simply salting your water for the 'soft-water feeling' then the less CH the better. Hard water has loads of Cal and Mag, and the less you have the softer the water.