Keplerian Proto-Arab Progress

[caters]

I am making a conlang called Keplerian Proto-Arab. Keplerian is because it is on a planet with Kepler in its name. Proto is because this is the first language of a language family. And Arab is because it is based off of Arabic but is not itself Arabic.

So the first step is the phonemic inventory and I already have the Arabic phonology for consonants in my phonemic inventory. Namely:

/m/
/n/
/p/
/b/
/t/
/tˤ/
/d/
/k/
/kˤ/
/q/
/ʔ/
/f/
/v/
/θ/
/ð/
/s/
/sˤ/
/z/
/zˤ/
/ʃ/
/x/
/ɣ/
/χ/
/ʁ/
/ħ/
/ʕ/
/h/
/d͡ʒ/
/l/
/ɫ/
/j/
/ɰ/
/r/

But should I add other consonants to it and what vowels should I add to it?

I do want the writing system to be either an alphabet or an abugida, I don't know which.