Nice one, @FILMon! Really cute characters too, very creative.
The structure of Tigrinya letters seems very similar to the Japanese Hiragana/Katakana systems with consonants are succeeded by a set order or vowels, see image below:
I’m sure there are hundreds of “Learn Hiragana” apps/programs which you could study for inspiration, if you’re struggling with “gameplay mechanics”. Or maybe @Tomires has some learnings, given his game Kanji Adventures.