I'm just a little bit ahead of you with my CS17 (#304), but I can tell you what I did with mine. I affixed the seat stringers in place to the side panels just before joining the two bottom/ side panel pairs together. I know it seems like it might make everything too stiff to bend them after that, but the planing you do to seat stringers forward of the forward bulkhead position gives them enough flexibility.
I put the inwales on after I had the hull 3D, squared, and the forward bulkhead and temporary bulkhead installed. It just took a little flexing to get them in to place. I chose to epoxy the inwales in and also threw in some 3/4" bronze screws on 8" centers from the outside for added measure. The screws might have been overkill but it seemed to me that since the inwales are the foundation for several attached structures, better safe then sorry.
You will be amazed at the difference the inwales make. The overall shape of the hull didn't seem quite right to me after I went 3D and wired everything together. The bow seemed too sharp and maybe even a little crooked. The inwales made the hull take on it's perfect "boat" shape.