: Is it easier to put the rudder on during the build and then not use it or and
: it only if it is needed after some time in the boat?

I am not a big fan of rudders or deployable skegs or fixed skegs.

Rudders have the advantage of controlling direction without interrupting your forward stroke. Even though a rudder adds drag the steady paddle cadence a rudder allows provides a net forward advantage. (Rudders are typical on racing kayaks.) The disadvantage of rudders are they cost money, they are vulnerable in surf, they break at the wrong times, they endanger paddlers in a wet exit, they make rear self-rescues dangerous, and endanger those providing assistance (re-entries)in rough conditions. They increase weathercocking when up assuring their use in wind.

Deployable skegs have the advantage of allowing the kayaker to select on the fly whether their kayak weathercocks, leecocks or is wind neutral to minimize the directional effect of wind and waves. Their disadvantages are they cost money, they will jam in the up position on a beach somewhere, and they require maintenance and repair.

Fixed skegs are added to kayaks that weathercock. Their advantage is they should be sized to create a wind neutral kayak to minimize correction strokes. Their disadvantage is they make the kayak harder to turn. Miss-loading cargo weight is a concern that will cause weathercocking or even leecocking and redistributing cargo weight is the required correction.

I feel a correctly designed kayak should be wind neutral without a rudder or skeg. The kayak will be maneuverable and have better speed because it will have enough aft keel in the water to eliminate the need for a skeg or rudder. Course corrections will be easier with a knee lift (edging) or easy paddle sweep. There are no mechanical moving parts that break or require maintenance. Proper cargo weigh distribution (fore and aft) will be necessary. (approx two lbs in aft hatch to one lb in the forward hatch).
So how do you build a wind neutral kayak? 1- Buy plans of a good tested design. Or 2- test paddle your kayak through an undersized rough cut cockpit cutout in a crosswind and move your seat to find its location that makes the kayak wind neutral (move aft to reduce weathercocking). Then locate the cockpit, coaming and rear bulkhead in relation to the seat location.

If you have a completed kayak that weathercocks, a little aft ballast will trim the kayak. A water bag under your aft deck deck rigging is an easy method to add and adjust trimming ballast. For a permanet fix for weathercocking I would move the seat back in the cockpit as much as is reasonable and if that is not enough I would add a deployable skeg.