Hey congrats! :O Kiliii is fantastic, you’ll love him (and love your new kayak! it’s such a transformative experience, getting to hand-build one for yourself!)!!! I’m not sure how much useful cold-weather paddling advice I have, since in my household the paddling season historically ends when September does, but I have kayaked in cold water, at least, and certainly done other winter sports. Exactly what you wear is going to depend a lot on the expected water and air temps, though, and expected conditions/location of the paddle.
I always wear neoprene booties under my Tevas in cold water, and I think they can be combined with wool socks for extra warmth- one of the things about a skin-on-frame kayak is that there is very little material between your body and the water, so even if your spray skirt is working fine you’re going to really feel the water temp anywhere your body touches the sides. I’d add a fleece between the farmer john and the drytop (ideally one that zips down the front so if you get too warm you can de-layer easily), and neoprene or fleece gloves as well. Wool hat or, better, one of those neoprene hoods divers wear.
Honestly your best bet for cold-weather paddling advice is going to be Kiliii himself though- you’ll have access to a real expert and should take advantage of him! I hope that was at least a little helpful, though (my father, who is much more expert than I, recommends an actual drysuit if you’re going to be paddling in below 45°F weather, although those are crazy expensive, and can be too hot when you’re in motion).