Okay, I thought that I'd add a few images of my garb as I go along. First of all, I've uploaded a picture of the underarm gussets before one side is sewn in: although they look square, they form very nice diamonds when completed and because they are one piece, are less prone to ripping under stress.

The other picture shows the triangular skirt gore as it is sewn in with flat-fell seams. On the inside, the extra fabric is folded over and over-stitched flat. The final effect is very nice and neat, with no threat of fraying. Lastly, there is an image of the whole thing inside out, before I began to sew up under the arms and flat-fell the seams.