Calculating the exact height of the glyphs for a given point size from the font metrics is complicated.
I recommend an empirical approach. — Just print your font at a large point size and measure it. Calculate the percentage change you need to get the desired result.
Without grid-fitting and hinting, getting staves to display evenly spaced at all point sizes will not be possible. There may be some drop-out at small sizes where some thin lines do not display at all. Design for a standard point size like 24 pt or 12 pt, and add hinting with a third-party program if you need it. FontCreator doesn’t yet support character hinting. Adding font smoothing tables may help.