Boat Builder Central

No, sorry. You need something for stiffness.
You could build it like a Carolina Skiff: with a very thick bottom, 4" of foam with longitudinal stiffeners in it. It would make the cockpit too shallow and increase cost.

For the fiberglass: what you show is fine. Don't worry about the gaps. You could use thinner glass but you have is fine. For the pintles (rudder pivots), 3/8" diameter is fine. Build the rudder first, put your pintles and gudgeons on dry and check against the transom. Offset one of the gudgeons...

It must be somewhere on the plans but anyway, let's build at a minimum 0.75" wide and 1" high. For a very sturdy one, go to 1" thick by 1.5" high.
When sailing hard, you will grab that rail often and for that reason, I like the thick one.
Sorry if it is not clear on the plans.

It should be included in the package. It is a simple drawing showing how to cut and frame a hatch for a locker in any small boat seat.
Reid has a temporary copy that I created for you, email him please.

The plans are not clear about that, sorry. The section at frame D shows a line all across as if the cockpit sole extended all the way to the sides but the cockpit sections show a "hanging" cockpit sole. Each way has pros and cons. The full sole extending all the way across is strong but re...

Tool or not, you can't have voids in there, Fill it with putty please.

I would not agonize over the exact shape and size of that radius. The putty is just part of the sandwich core, the strength comes the tape and later, from the wide fabric overlaps. As long as there is no air in the seam, you will be fine. The main point to focus on is to avoid air bubbles. Even a ve...

This is a lot of calculations for something that will change all the time but I admit, it's part of the boatbuilding fun to speculate about those things. :D The CLR is 2D but not all parts of sail pull the same way, for that reason and For even more fun, I recommend to add an ingredient: lead. Lead ...

It depends. Fort example, a 8" wide (20 cm) side deck along the cockpit, with braces spaced 1 meter, will flex exceedingly but the same side deck with and integral coaming will be very stiff and you could walk on it.

I don't have the plans with me but there are two offsets for very large parts. The smallest one is the keel (bottom panel).
There is another way to check which part is which: the width of the transom, along the bottom edge, must match the keel width at the transom.