1/8" and 3/16" is all you need for edge guide feet. 1/4" will give you a very wide ugly french seam.

Aside from your piping and zipper feet, that's all you'll need

I've got the full set.Its surprising the uses for them, not only french seams.I make a lot of tool rolls and the 1/4 inch makes a nice folded seam or you can use on a single stitch machine to make 1/4 parallel lines on a seat or door panel.

I've got the set of 3 right side guides. I use the 1/4" for sewing binding on carpet. I also have a left side 3/16" guide. Comes in handy for the other side of the French seam when the cover is too much to cram under the machine. Also a standard welt foot for welt and a 1/2" welt foot to sew windlace.