Well, perhaps not absolutely everything, but I found this incredibly useful paper that cleared up quite a few of my questions in plain language: The Development and Design of Bronze Ordnance, Sixteenth through Nineteenth Centuries.
I now know that the profusion of names for big guns across different cultures, times and authors does not necessarily mean that there is no system at all. Part of the problem is that some authors use a term as a specific name and others use that same term to mean a category. Culverin, for example, is often used to name a specific gun, but more generally should be used to describe a category of gun: those with calibres of 32 lengths or greater. Cannon, as a category, are those guns of calibres 15 to 28 long. So calling something a culverin cannon makes no sense.
A saker, a common battlefield gun, was a culverin throwing a typical weight of shot: 4 3/4 to 7pdr.
A battlefield gun, culverin, could be of any weight of shot and this leads to the wide variety of names, but the crucial thing is the ratio of the length of barrel to bore, giving them higher velocities and flatter trajectories.
This is a great help to me in writing Forged in Blood as I want to use terms that will make sense and not cause a reader with advanced knowledge to be offended.