The circular curve of the underarm cut is important to achieve the fold fullness. Do not cut the arm slit until you have sewn the side seams. You need to mark the slit site which will be inside the natural fold of the dress as worn. Stitching Finds indicate running or back stitch for seams, stitch length 2-3mm. Unfortunately not many modern wools are fulled, and linen always needs seam finishing.
French seams are a good way and evidence supports their use.
Hemming is again by running stitch on a single fold or by a double fold help by a catch stitch . Men Here is an illustration of a similar garment for men.