It might be nice to brainstorm this issue a bit. We developed a system of dowelling that made for very tight joints and fairly easy assembly in the small production shop environment. We use a mortise and tenon construction, but with cope and stick cuts. We only use the long tenons on the rails. I use a Maka mortiser and a Wadkin BEM shaper for the tenons and panels.
Profiles are standard.
We use a JL Lancaster frame clamp for assembly. And since most custom doors are high-end, this seems to be what customers expect. I think the first post has the right idea with the male and female pattern plus dowels. That s typically how most doors that I have used are constructed. Likewise, pretty much all commercial stuff is at least 7 -0 .