I was going to make a new suggestion about this same topic, and I seem to have already done that long time ago. Sorry for a super long delay.
I think the initial suggestion still holds, and my suggestion is to specify the number in font info; isFixedPitch to have a number field where zero is considered OFF and any non-zero value is considered True as well as the layer width (and there is no need for a checkbox in a boolean custom parameter since you can now dis/able them from the left checkbox). Linking the width to a particular glyph doesn’t sound user-friendly to me (feels like the lowercase d issue in Illustrator).