There were a couple of questions I know the answer to.

Foam Core Dagger boards being too thick - The foam core is cut to accommodate the skin.i.e. the foam core is made thinner than the final shape. For many shapes the trailing edge ends up solid and has to be tapered by hand or use a modified Blount trailing edge or what is called an interrupted foil. The interrupted foil is where the design foil is a little longer than you want. You interrupt the foil to have a 2-3mm thick, Blount, sharp edge, trailing edge. Verbally, test people tell me this will have minimal impact except at high angles of attack and less impact than a chewed up fragile edge

Foam Core Not Strong Enough - On the board I cut by hand I am using 6 lb/ft3 Styrofoam with ~1mm carbon-Kevlar-carbon skin. I would not want to jump up and down on it but it will hold my weight. The RC method for handling the strength issue is to cut the core longitudinally every x inches or so. Replace the foam lost from cutting (1-3 mm) with carbon. This gives you longitudinal ribs and makes the structure strong enough to jump up and down on. I have been told the quick way to make the ribs is to make 48"x6"x1/8" carbon up in advance then cut out what you need on a table saw.

In terms of materials I found 45x45 degree carbon - 90x90 kevlar - 45x45 carbon - 1.0 oz 90x90 glass to work and required minimal finish work. The board I made with uni carbon may be stronger but it was a lot more difficult to finish. I will never use Uni carbon held with monofilament again.

I agree that cedar core would be stronger. I have built both. My one summer of use has shown the carbon foam to be strong enough and it terms of time and money I would cry a lot less if I had to replace a carbon foam board.