What should I start with?

[Aishah]

I have never read any of those books before but since your into the Shatter me series, I'd probably recommend you to read Restore Me.

[Rorro]

I'd say Restore me too
Then ACOTAR and finally powerless

[Eli (taylor's version)]

Restore me OF CORUSE (Hope you love the series as much as I did )

[Scout ੈ✩‧₊˚]

i havent read the shatter me series, but acotar is pretty good :D