Sins can only be comprehended with a fully Christian mind set (Truthfully and Objectively Catholic or Orthodox). Evidence of this; if you believe you are more correct than the Bible is self idolatry.
I do not how ever blame you, Christianity is a mystery until you comprehend the meaning of Christ and his sacrifice. So your question here
>Is it wrong to believe in an omniscient "God" of sorts, but without conforming to many of the strict Christian teachings?
It is only wrong as so far as you deny the truth. You cannot yet be blaimed for this seperation of truth and self-idealogy. You are afflicted by the ways of the world, yoy may blame the time of "enlightenment" on this if you wish (you should it is the truth).
God comming forth as men presented a new revalation of man. He was the God of all, and he was loving of all. He in the flesh, Jesus Christ the man taught what sin truly was, it was the disobeying of God in the heart. I know you may not see this quite yet, but when we masturbate we are doing nothing but fulfilling our passions of flesh.
An important thing to note; God is all purposeful. Everything he does he does for a purpose, and for every purpose there is he fulfills. There is no purpose for masturbation, and as such it denies God in the heart. (Note; purpose in the context of Holy Fulfilment)
You should obey the Bible, as the Bible is the only way of knowing the Word, as the word made flesh. It'll bring light to the truth that was written on your heart, for you where made in God's image, and you where to fulfill his purpose as he would fulfill his purpose on earth.
Be like Christ anon, and you'll be unbound by the reflection of your flesh.