Hi Dr Mark,
Welcome to SoS. Your posting is a new thread and hence it is the correct place, but you could also create a build log and post questions about your build on that thread too.
The term for a recess along the keel is a
rabbet, not to be confused with a long eared mammal that in Australia is a pest and hunted, a
rabbit.
Most builders who create the rabbet do so by sanding or using a burr to rough out the long trench that the planks ends fit in to. There are
tools specifically designed to rout out a rabbet but most are oversized for ship modeling. You could also use a narrow chisel which like most things in model shipbuilding requires considerable patience and attention to detail.
Ideally the rabbet contour should accept the corner of the plank and tends to be a triangular shape. The depth should be equal to the thickness of the planks to create a flush finish with the keel, although some sanding will inevitably be required to achieve a seamless finish. The glue should not add to the thickness and if it does you have used too much glue.