I have also started to explore this venue of editing TTF fonts to add custom symbols (working on a font for Genesys ruleset and another to update Star Wars Ruleset) and i have recently have made progress, making a somewhat working font, both for classic and unity

I used FontForge, and here is a link to a very good basic tutorial which helped me a lot:


I have not created the symbols from scratch, I copied them from different font files, so in my case it is easier in some parts (just needed to import and change the size parameters), but causing difficulties in others (had a lot of errors since the font symbols seem to contain issues like unconnected lines)

These issues i fixed with this tutorial


After you edit the font, you can test it in winword or another editor, and in order to add the symbols, you can use this windows app "Character Map", instead of typing alt commands (also work to input to fantasygrounds)

By no means i think the above is all you need, but i hope it helps you to start, like me

If I have any progress, i will let you know also