A lot of the problems arise because every shape has its own special considerations that must be taken into account. Too bad I don't have my molds any longer. Hey, no problem. I have a turned balsa nose cone that I don't trust lasting a launch. Big problem with using balsa wood for mold models it the fact that balsa is not dimensionally stable and changes in temperature and humidity will cause the wood to swell and change shape.
Balsa is a good core material but it needs a good fiberglass skin to give it some strength.
Best thing to do on a hand build up is to cut the core undersize and then lay the glass on top of it. I would like to develop a reusable mold for casting my own cones. We may have to cover this in several installments. I have never tried this before, nor has anyone I know locally. To get some first hand experience, check locally for fiberglass boat builders, race car builders or small aircraft builders.