Redwood will fade to a pleasing silver tone in natural light. It is prefectly acceptable to leave it like this.
You can stain your bench any colour using a water based wood furniture stain. (Follow manufacturers instructions).
It is not uncommon, in Redwood, for small splits or shakes to occur in the timber or slight warping in quick drying weather conditions. These will normally go back when humidity rises. This is nature at work and is perfectly normal. It does not affect the strength and durability of your furniture.