From the gunwale angle described it seems that you are building a "typical" Greenland style sof kayak.

Of course gunwale angle alone cannot be used as a guide to achieving how a certain kayak will behave. Some of the things involved in designing a kayak are beam , waterline beam at a given weight, length overall , waterline length, chine placement , gunwale angle, depth to sheer, dead rise, rocker and cockpit placement.

If all things are equal then the kayak with a greater gunwale angle will be less stable initially as this makes the bottom narrower. Secondary stability in 20" beam and less sof Greenland kayaks is so dependent on the paddler that inherent secondary stability of the kayak is of little importance. Remember these are narrow kayaks!

Not being familiar with the plan I cannot say for certain what dts you should aim for to have a fairly low rear deck and a decent free board but it will be in the 8" dts range at your bodyweight.

As this is your first sof kayak I would STRONGLY recommend you follow the directions of the plan you are using.

Best Wishes