1 . Call it a CC BY-SA license.
2. The words I printed in the book are meant to be used as examples, but I'd be careful about allowing synonyms with no constraints, as that could potentially drastically affect how players approach harmonics. I would allow only "synonyms" that significantly increase the specificity of the word listed, so Insect -> Bee would be fine but Flame -> Blaze would be a little dicey. Beyond that, players could be allowed to rename their spells however they like so long as that name doesn't affect the underlying words used or the "flavor" they evoke. Like, if a player wanted to say that the spell made from (i.e. harmonics were calculated from) the words "flame" and "beam" is called "Blaze Beam" because it sounds cooler, that's fine.
3. It's true that d4's are optimal for most implementations of spell damage (more accurately, when seeking to maximize the average roll total to harmony ratio). The Detriment Rule is the main reason for other die sizes' inclusion in the damage tree. In general, this tree will vary greatly in use case from system to system, just because HP/player resource systems in general vary pretty widely.