The French Curve is just a ruler that helps you to draw curves when working by hand. Professional pattern makers learn (with experience) to draft these curves by hand - without the need for extra rulers.
When drawing curves, one needs to bare in mind that if the start and end angles are not at a 90° or 180° angle to a seam, it will result in a peak or valley once the pattern pieces are sewn together. With this in mind, always check where you are drafting the curve and use the connecting edge as the formula for the curve handle, adding or subtracting the 90/180° as needed.
The length of the curve handle depends on the length of the area that the curve needs to travel before changing direction to form the curve. Normally, 2 sides lines are drafted before one drafts the curve, so I use the 2 side lines divided by 2 for the respective lengths of the curve handles.
I hope this sheds some light (theory) on the matter.
I do suggest that you download and install tomorrow’s weekly update It has an amazing change to simplify drafting curves, which you may read about in this topic: Auto-Smooth & Force Length (Code available, looking for dev help)
I’m wishing you all the best with your clothing company venture.