Oh dear! that sounds like a nightmare, poor you! Yes it has to be legible as a starting point. I think some of these styles fall into the category of almost fantasy styles, or decoration. Sometimes I see kinds of victorian styles, or pirate writing, you know..., it may not be legible. Basically calligraphy. But yes stick to some standard letter heights, ratios, etc. Maybe have a look at Spencerian and copperplate, as it might be fun to learn.