When wine undergoes malo-lactic fermentation, the malic bacteria will digest the sorbate and produce geraniol, a geranium smell that is difficult or impossible to get rid of. Malo-lactic fermentation is almost universal in red wines made from grapes, so using sorbate in those wines is usually not a good idea. Also, you should avoid using kit wines (that contain sorbate) to top-up carboys or barrels of red grape wines that will or have undergone malo-lactic fermentation. Even a relatively small amount of sorbate can have a serious effect.
No - most wine yeasts are resistant to sulfites. Sulfites are often added at crush, to discourage wild yeasts and other spoilage micro-organisms, while the desired wine yeast gets established. Sulfites are generally used after fermentation, to prevent oxidation of the wine in storage.