Woodcraft is the place if you want to carve 1-5 decoys only. If you are looking for a rig, you will need to find a cheaper source of timber (unless you are Dave "sitting on a gold mine" Parks) they will get you in the game to start. Basswood is another wood that can/is used, but where you are located the cedar or white/sugar pine is probably a better option. Heck, some guys use red cedar (beware of the dust!!!)
Knots: tight? leave um, if they are smaller. Loose, cut them out and plug them with a plug of scrap then align the grain, use epoxy.
bondo: I would not use this. many guys have used this in the past on neck joints, only to have it fail down the road. JMO
I don't use hot glue, just 2 screws that I run up from the bottom, obviously short enough to NOT be cut by the bandsaw. They get hidden when you place the keel anyhow.