Inma - Many thanks for this useful lesson.
I am wondering if it might be worth emphasising, at the beginning, that "-ar" verbs all form their gerund quite regularly. Is that true?
That could be reinforced with examples like pensar [> pienso] > pensando;
and (in your category 3): contar [>cuento] > contando.
and maybe even mention in your category 1 that crear > creando is quite regular - (i.e., with no 'y' inserted).
We do appreciate your hard work and dedication !