My own opinions.

If you are discussing a Prince Charlie jacket specifically, as these typically are sold as a unit with a 3-button waistcoat, that is the first recommendation. Though many of the pictures posted show a PC worn with a belt and waistplate (sans vest), I personally don't think this looks as nice. I have seen the PC worn with a black cummerbund and I think this looks fine.

I'll throw my hat in with those who do not favor the 5-button waistcoat with the PC. If you want to wear it, fine, but realize that it is a modern, somewhat "trendy" look, and not the classic style. I say if you want to wear a 5-button waistcoat, get an Argyle jacket to wear with it.

As for the Sherrifmuir doublet, it was interesting to me to see a few pictures of this style posted here with no waistcoat. One almost always seen this style worn with a waistcoat of some type (either solid or tartan), and most often a high 5-button waistcoat.

I am personally a fan of waistcoats. I think they can be slimming and really add a lot to an outfit.