I've finished the core - it was 3-4mm at the tips, and ~9mm at the center. Gradual thinning was done starting around 5cm from the pads area - hopefully that doesn't compromise the strength of the core too much.
Then, I've done the rails. It was messy as f***, infusion epoxy gets into every tiny little hole there is. I've used a PVC blank as base, and a cutout of a real board in same PVC sheet. Laid it down, pressed it down with bricks, then poured epoxy + 10% of carbon fiber powder mix into the rails. It started coming out from every possible hole there was, had to move it onto a plexi sheet to avoid damaging my living room floor
Putting the inserts failed miserably as well - I should have secured the bottom with a tape first, now half of the epoxy just bled out onto the bottom. Separating the outline PVC board from the bottom wasn't trivial either - cut my fingers couple of times - epoxy+carbon is sharp! Destroyed the bottom PVC board when doing that, too - it broke in a couple of places. Other than that, the rail is pretty tough - made a few samples, tried to break them with a hammer - no luck. Will use the same compound to pour fin holders and fins themselves, just for fun.
Now, I need to sand off the extra epoxy and trim the rail (outline moved during the rescue-the-floor phase) to something like 5-6mm. Gotta get myself a respirator for that, carbon dust is bad for your lungs I hear.
Other than that, I'm quite happy with the result. Sanding and pouring the inserts (again) tomorrow, and laminating (hopefully) in a couple of days. With luck, I should be able to test drive it over the weekend!
not final, I thinned it quite a bit more
playing Queen - Under pressure ft David Bowie in the background
bottom - dat bleed radius
insert, barely stuck with all the epoxy that bled out