Stewmac in the US sell a fret saw with stops to limit the depth of cut, that's one way of doing it, but it's an expensive saw compared to my el-cheapo one. I rely on judgment and I count the strokes of the saw - the one I use cuts on the pullstroke and it is quite agressive, maybe three short strokes is enough. Once I've put the fingerboard through the slotting jig I can make final adjustments at any stage - the jig spaces the frets correctly and keeps them square to the centre line and parallel to each other. Of course, if you make a bound neck, it would hide the slots and it wouldn't matter then how deep they were. As far as I know, guitar manufacturers use either a CNC router or a multi-bladed table saw to cut the slots. Some of the best American builders on tdpri.com use radial arm saws or table saws, and again, Stewmac sell a thin-kerf circular saw blade. Only the CNC machine could cut a slot that would follow the camber of the fretboard.
You are right too on fretboard radius, 12" is common, but anything from 9" to 14" would be ok too. Some guys try to achieve compound radii so that the fretboard becomes a section of a cone, I haven't done that either, and I have no longing to try ;-)