Actually, the pockets on that jacket seem plenty high for a kilt jacket conversion; though the actual pocket may need to be shortened slightly, they should still be sufficiently deep to keep things in and not look too close to the lower edge.

As for the angle, I've found when I want to make a good rounded edge on anything, the best thing to do is find a cup, plate, bowl, etc. of the right size and trace around the edge of it to make a perfect curve. While this may still leave the separation of the opening a bit low for your kilt jacket, it should prevent the "sharp-angled" look from which many converted jackets suffer.

Good luck, and I'm anxious to see how it turns out!