Many paddlers tape pads into their ski's buckets. A pad can help create a better angle and therefore more leverage at the catch, as well as provide comfort and/or a more snug fit which can increase boat control. Paddle2Fitness seat pads for efficiency. See also Padding in Equipment Adjustment (padding for fit and comfort)
You may set your foot braces for different conditions. In big waves, you might want to set your braces long so you can get your weight lower in the ski for added stability. In flatwater, you may like to shorten your braces so you can exert more torque.
Hand Position - Hayley Nixon
Setting Up Your Grip - Nicholas Cryder
In general, paddle length depends on torso length when sitting in your boat. At the catch, with the blade fully submerged, you want your upper hand at about forehead height. Get a friend to watch you and help you adjust your length. (Oscar Chalupsky talks about using an advanced technique of changing his paddle length mid-run. e.g. getting tired? - shorten the paddle, feeling strong? - lengthen the paddle. This technique would obviously require practice. Who besides Oscar regularly employs it?)
The number of degrees to which you set your feather is personal. The traditional standard has been 60 degree feather. Oscar Chalupsky has been an advocate of starting paddlers at 0 feather for some time. The advantages of no feathering include making it easier to brace on both sides, and possibly reducing strain on your wrists (some report the opposite to be true). But a strong majority of paddlers currently do not support zero feather. One disadvantage of no feather is wind resistance on the blade going up-wind.