To what extent do we as humans have free will and to what extent has God predestined our lives?
I have a couple of comments on your position.
First I would address what you said about omniscience.
countryroadmusic said -
Simply stated - it would seem to me that unless this is true - then God could not be truly omniscient
But then you could just a simply state that unless it is true that God can destroy the world anyway He wants He is not truly omnipotent (all powerful) - yet we know that He has limited Himself so as to never again destroy the world through flood. So I don't think this argument is sound.
Ask yourself - do we consider God to be less than omnipotent simply because He has chosen to limit Himself in this way? No, of course not. So we should not consider God to be less than omniscient just because He has chosen to limit His foreknowledge so as to make His gift of free will to us truly free.
Secondly I would say that just because something doesn't appear obvious to you in the scriptures does not mean that it is not obvious. It may just be that you do not understand it fully yet, because you have not done enough research. This is an ok position to be in, since no one will ever do all the research needed to understand all of God's word. But we should not be lax in our efforts or ever settle for this state and say it is good enough, and I know you were not saying that we should rest on our laurels.
Of course even in the ones you list as obviously clear, others will find a difference of opinion with you on. For instance the issue of adultery is not one you would find agreement with Messianic Jews. For that matter even the definition of adultery is not the same among mainline Christian denominations, as some hold it to be merely looking on a woman with lust while others limit it to the act itself. Those are of course details and can be argued themselves, but I use it to show that not everyone who reads the scriptures sees everything as being as clear as everyone else does.
Thirdly, I think there is a danger, you may not have realized was there, in the idea of accepting your understanding of predestination, even though admitting you cannot prove it is absolutely correct. That danger is that other doctrines end up being based on these unprovable doctrines (such as predestination) that we formulate without a clear ability to reconcile all the verses in question. For instance the doctrine of "once saved always saved" can be very closely tied to the idea of predestination. I don't know if you do this or not but some do. So suddenly predestination is not something of little consequence that God would not want us to have a complete understanding of. Instead it becomes a salvation issue and one we should have a full understanding of in terms of how to reconcile it to all scripture.
Check in your own system of doctrine and make sure these same verses that give you problems with your position on predestination do not give you problems in other doctrines that are related, such as I described above. If your systematic theology can reconcile all the verses in question then you should be content, but if it cannot, and there are problems even with the essential doctrines related to salvation then maybe you were too quick to become satisfied with not knowing the answer to these difficult verses.