Nice work. Another way to do inside corners is take the panel headed into the corner and bend it at a 90....then put J channel against that panel. Just using one pce of J and looks clean. If its protected from rain you could skip the 90 bend on panel headed into corner and maybe lap tape the j to the panel or good sealant, just don't let it ooze out. I'd sleave the joints of J on the outside corners so water cannot seep in the crack. But we don't use J on outside corners we make a corner trim that goes over both sides 4 inches.

Ive always put inside/outside corner trims in one piece and then had my windows have both window sill and header flashings with the window sill being 1.5" past the ends with end dams so the J can sit inside there and then the window header is made up to be the same width as the window and my J's are ran over and up around like a upside down "U". in my opinion it looks cleaner that way. especially if youre needing to run the panels horizontally instead of vertically

Any reason to hem the bottom of the panels to have them lay flatter on the drip edge? Does it bulge there?

What is the panel width?