All the information is there - yes really - you just need to explore and find it, (and learn a new language). By all accounts John Brooks' plans are extremely details and come equipped with cut lists, materials lists and building specifications. In conjunction with John's book Glued Lapstrake Wooden Boats, one can find answers to every question. But you do need to look hard, especially for a first timer. Having sent a few emails to my fellow workshop class mates, and receiving patient replies I began to realize that indeed all the information is on the plans...
Half breadths...yes that is an interesting concept, once you have made a stem exactly half as narrow as it should be (I didn't, but very nearly did!). Most of the plans show measurements as half widths from the centreline. The logic I presume is to ensure complete symmetry. John is quite encouraging to his students about mistakes - as long as they are the same on both sides of the boat, no one may ever know...
Also I began to understand that when John writes his instructions they are exact and precise. So when he says to build the inner stem and then shape to the Full Size Plan (FSP to you boat builders) and THEN laminate the outer stem over the inner stem, if you decide to simply laminate the outer stem over the inner stem before refining the shape of the inner stem, you end up with an outer stem which is out of shape...oh well, I am optimistic that I can get the outer stem to bend into shape, if not I can build a jig again for the outer stem in due course.
Plans can be unwieldy and so for the early stages of my build I had them rolled up in the corner of my workshop pulling one out when I needed it - and could reach it. So the big learning for me was to cut a large 3'x4' hardboard and use paper clamps to hold the plans on the board for easy access.