Clew plate on the jib, Which hole and why? Do you choose one over another for different wind conditions?
Changing sheet attachment hole on the clew plate changes the angle of the jib sheet - closer to the leech puts more tension on the leech (and makes the sail a bit fuller); closer to the foot puts more tension on the foot (and makes the sail a bit flatter). Flatter is better on the jib - it helps with pointing ability.
In general, you want it as low (closer to the foot) as possible and still able to sheet the sail in all the way. Most racers will put the bow of the shackle through the 2nd bottom hole and the pin through the third (middle) hole with the blocks hung off either side.
Batten Tension, for the non racer does any one change the tension for different wind conditions? From what I understand looser for high winds and tight for light wind.
Batten tension affects the fullness (draft) and the position of maximum draft. Tighter battens will make the sail fuller and move the draft forward.
The basic setting is just snug enough to pull the wrinkles out. Sight up the sail to make sure they all have the basic shape (the battens are parallel to each other). Once you find that point, mark the battens with a Sharpie so you can adjust to the mark in the future.
On the jib, the battens are pretty much set and forget. They shouldn't have much tension, and often the ends are taped to prevent snagging on the mast/halyards.
On the main, the battens need to be snug - a bit more than snug for the top 3. Always loosen the battens when you're done sailing.
Racers will put a lot of batten tension on in lighter air / lumpy water. A fuller sail has more power at the expense of pointing ability.