:salam2:
Brother there are 6 pillars of imam if any of them are missing person is no longer muslim.
Believe in Allah,in his Angles,Books,Messengers,day of judgement and all Good and Bad comes from Allah.If someone denies any of the prophets hes no longer to be called Muslim and vice versia.
Now as the talk comes to books etc whatever is mention in Quran should be followed.Anything told not to do is simply kufr
Secondly there are 2 types of shirk one is shirk al akbar and shirk al asghar.
In shirk Al Akbar there are again 3 things
In Rububīyah {Lordship}
In al Asma was-Sifat (the names and attributes)
In al Ibadah (worship)
The shirk al akbar completely removes a person from the religion .
I cannot completely comment on this so i would suggest you reading thing book by Sheikh Abdul Wahab
The Book of Monotheism
you can either buy it and read it here will clear your mind InshAllah
http://www.kalamullah.com/Books/kitab_ut_tawheed.pdf