Seconded. The company I work for is currently commissioning a custom family of fonts from a major digital type foundry... and it's a vast (and expensive) undertaking. Consider potentially important features like support for[1]:

    font-variant-numeric: tabular-nums

For fonts with the support coded in, this variant means numbers in tables will line up in your font without outright switching to a monospace font. Beyond good glyph design, as the parent mentions, there's a lot of work to craft a professional modern font esp. the more of the Unicode language space it spans.

[1] https://developer.mozilla.org/en-US/docs/Web/CSS/font-varian...