Carbon on the outside is very vunerable to chafe and wear from beaching etc, put a layer or even two or 3 in the susceptable areas such as the bottom and trapezeing feet areas of glass. It won't add much weight as it has the benefit of mopping up the excess resin from the carbon layup.
I simply wet out the carbon and then place a layer of glass over the top, squeegee ( using a plastic filler applier )the glass into the carbon and you can soon see if you need more or less resin. I tend to layup a heavy glass cloth and then a very fine layer as this tends to flatten out the twill and therefore you need less filler and paint. Enevitably when you are fairing the outside before painting you can rub through the glass but it is obvious where as the carbon is not and much easier to repair.
In relation to the beam, it really depends on whether you are intending to be a single hander or double. If single then you can place the beam way back as per the A Class but with a two hander it becomes impractical as you need to be able to get the crew through under the sail, Bitsa is a bit extreme and even single handed it is tight. There are other benefits to having the beams back such as you need less volume up front and in theory should be a better light air performer without sacrificing Spinny down wind safety. Again Bitsa seems really difficult to bury the front as the Spinny clew is only about 1 metre ahead of the front of the hull even with max length pole.
The rear beam is much more tricky as it is really dependant on your rudder system and how long the arms of the rudder connection bar is. The system I used of gantrying out the rudders is too time consuming and I'm not sure that practical. Stick with the conventional I would say. Fire the questions off as I'm sure there will be an answer.
