In my quest to create a language for some fictional characters of mine, I came across nonconcatenative morphology like triconsonantal roots. If I wanted to employ this in my conlang, how many consonants must I have? I see Arabic and Hebrew, for example, have at least 25 consonants. Could I use fewer?
It's a matter of combinatorics; if all your roots have three consonants, then you can have n^3 different roots; with ten consonants that would be 1000. (This assumes that all combinations are valid/usable). With 25 consonants you'd be at 15,625. If you add more variation, ie add biconsonantal roots as well, you can increase the number a bit.
So I would start off by thinking about the inventory you need, and then work backwards from there. But don't forget that 'root' is not the same as 'word': it would be more like 'concept': once you add vowels in between the consonants, your total number of words will be a lot more than the number of roots.