Words can't start and end with any letter. There are select letters in which words start with and what they are next to.

>With consonants<
A word can start with: b, ç, f, h, j, k, q, s, t, v, w, y, and ⱬ.
A word can end with: ç, d, f, g, j, l, m, n, p, q, r, s, ş, t, v, and ⱬ.

>With Vowels<
A word can start and end with any vowel, but not with a vowel pairing.
A vowel pairing is only made with two vowels of the same letter side-by-side (like ee, for example).
But a word can't be entirely made from vowels.

>If Ǫǫ is implemented<
Ǫǫ can't start or end a word, nor can it be paired.
However, it is a wild card vowel.