Scalable fonts use a relative measurement system called units. One unit is a thousandth of the font size (or em). But you can set it to something else with the Units per Em setting in File > Font Info > Font.
So you need to decide on a font size, then you can make the calculations.
If you want the values to be the same on different sizes, you can either interpolate or if you have a monoline construction, offset the path with a custom parameter.
Exactly. The size in which a font is set cannot be controlled through the font. That is the job of the app in which you are using it, CAD in your case, I suppose.
What you can do, is optimize your font for certain sizes, e.g. choose a stroke thickness that is exactly right if the font is set at size x. But you will still have to set the size in CAD.