There are lots of inflatable kayak bags available for just that reason. I'd consider them a good investment as they will be very form fitting for your boat.They are often used in damaged/leaking boats as they keep most of the water out. And, depending on how ambitious you are, you cold make a couple of bulkheads and cut and install some hatch covers.Def
2 part epoxy should do well enough for the leak in the seam.You could tidy the rough edge a bit, put some resin around it to create a non-fibrous edge of hell.Put some pinch moulding around it, it looks good and will protect the edge of the GRP.
You can dip some paper strips in epoxy and feed it into/through the cracks and it will leave epoxy behind.Most fiberglass, kevlar or carbon fiber boats will have a silicone or rubber strip around the seam on the outside. It's usually referred to as a rub rail and there is a lot published about it online.Def