IPA
Vowels

Consonants

Credits to @disco_n0stalgia for the above graphs
Writing system & words
Everything about the writing system and words can be found in
Atinmosi.pdf (3.1MB).
I apologise for the terrible handwriting in advance...
phonotactics
- CCVCC
- No double letters allowed, split them using "q" like "ll" → "lql"
- For double vowels, just use the long vowel, like aa → á
- ñ is always followed by a vowel
Numbers
Atinú uses decimal numbers, the symbols are already in the PDF, but here is a chart for reference:

To write numbers larger than 10 in words, just write it like X(o)ðuzatY [X: number in tens place, Y: number in ones place].
Add the "o" between X and ðuz when the last letter of X is a consonant.
Optionally, add the "o" if the last letter of X is an "e" if you want to sound fancy.
Examples: 11 = ðuzatun, 20 = doðuz, 22 = doðuzatdo, 30 = þreðuz/þreoðuz, 40 = catroðuz
100 is hijon,
X00 is just X hijon, not one word like Xðuz,
X0Y is X hijonatY.
Examples: 200 = do hijon, 222 = do hijon doðuzatdo, 300 = þre hijon, 404 = catr hijonatcatr
Rest of the bigger numbers follow the same rules as hijon.
1000 is kiro,
Million is mili,
Billion is bili,
And trillion is... you guessed it! trili.
Also here's an example of a big number: 9,234,567,891 = "nove bili do hijon þreoðuzatcatr mili fuif hijon rogúðuzatsyþ kiro ojo hijon noveoðuzatun".
Looks complicated but its literally the same as english, "nine billion two hundred thirty-four million five hundred sixty-seven thousand eight hundred ninety-one" :P