In many respects, how best to join the hull and deck depends on whether or not you are installing hatches and/or bulkheads.

If you are doing hatches, cutting the openings before the joining will give you access and make it much easier to reach the very bow and stern when you tape the seam.

If you are doing bulkheads and hatches, the bulkheads are much easier to install prior to the joining.  I then use the hatch openings to tape the deck/hull seam and fillet the top of the bulkheads after joining.

If you are doing bulkheads without hatches, you will have to install the bulkheads after mating/taping the entire seam via the cockpit opening.  Not taping large sections of the hull/deck seam is a bad idea structurally.  If you are going this route, you may find foam bulkheads easier to fit and install after mating.

Neither bulkheads nor hatches are required, but IMHO both make sense in a boat like the NH.  The bulkheads are important safety features which provide floatation and limit the amount of water in the boat if you get swamped.  You can use floatation bags instead of bulkheads for floatation but you will still have more water to pump out than with bulkheads.  Beside storage, hatches provide much easier access to the ends of the boat for construction, inspection and repair.  I think that it is a bad idea to have a completely sealed section in any boat that cannot be inspected and allowed to vent/dry out.  Any water that accumulates will eventually lead to problems.  I have had great luck with the CLC flush hatch kit but the Sea-Lect hatches will be more water-tight if you plan on doing a lot of surfing and/or rolling.

   Air Bags........My bulkhead equiped kayaks  have never popped a hose off the bag fitting, gotten a small hole in the bag, or had a leaky valve, but my air bag equiped kayak has.  A proper fitted and inflated air bag can significantly reduce the amount of water in the boat.  The bag can make assisted and self rescues possible.  A kayak without floatation fore and aft cannot self rescue in normal water.  

>>>>>The book that came w/ the kit does not mention bulkheads, and I have not found the answer elsewhere>>>>>

There's a not unpersuasive argument that rigid plywood bulkheads in kayaks create a stress riser or hard point that, by inhibiting flexing, can result in hull damage.  Say, when sliding over a rock or something.  

For this reason, some kayak designs specify minicel foam bulkheads instead of plywood bulkheads.  The Night Heron SG is one such boat.

While that approach has technical merit, in 22 years I can't remember a single incidence of a hull breach that could be correlated with the presence of plywood bulkheads.  So we've been using plywood bulkheads for ages.  You could certainly use plywood in the Night Heron SG.

Thank you, all!

So, just to double check, the "interior temporary forms" (#2 and #4) are the bulkheads? Before joining, it does not seem like they are going to fit right...