WKAS Br. Dawood!
Thanks for your good wishes and I also pray to Allah "May Allah increase me in knowledge and good deed".
Dear Brother Dawood, I knew the context of those Ayats which I quoted and to which you drew my attention, but I think I failed to draw your attention properly towards the mode of the answer. It is just not the wrong practice which God rejected but the excuse of hiding behind ancestor itself was rebuked by God, particularly in 2:170.
I will quote again "…….'Follow what God has revealed', they say, 'Nay! We will follow the ways of ancestor.' Here God first refute the argument itself then the reason for refutation "…….. What! Even though their ancestors (and the ancient Imams) were lacking in understanding and were not rightly guided?"
Further, again I would like to draw your attention towards mode of answer besides the context in 43:21-22. In 43:21 God is asking "What! Have We given them a scripture before this to which they are holding fast?" clearly shows that God expects "scripture" as defense not "ancestor" as in 43:22 "Nay, but they say, “We found our fathers following a certain religion, and we find our way in their footprints.”
Now, regarding your question - If Quran is silent on something, how can you use Quran to decide what is right and wrong? An example is the call for prayers. Quran is silent on its words as well as the mode/manner of delivery, yet this call is well-known to Muslims.
My answer is, yes if Quran is silent on something than we cannot use Quran to decide what is right and wrong. Any decision on that matter will be the decision of human beings which can be changed or altered according to the time and circumstances, not of God which is unchangeable and unalterable. So 'Azan - call for prayers' can be given sanctity based on its historicity or in its beauty of words or in its attention drawing power but it cannot be claimed that this 'Azan' is sanctioned by God. Be careful Dawood Bhai, any argument against this will lead you to quagmire of Shia and Sunn - whose Azan is sanctioned by God Sunni's or Shia's and I know you are fully aware of the differences. Those differences are not minor one like "rafadain" of Namaz.
On your second question "Can you use Quran to pick the Halal and Haram (if any) from it?" I think it is sufficient to say that you yourself have answered in point 2 of your post. So need of my answer.
Regarding your insistence on "Creed of Ibrahim", Sir Jawaid has explained in detail and he is persistently asking you a direct question from where you are getting 'Ibrahimic Creed' but you always divert his questions and trying your best to make us believe that some of rituals/rites from the time of Prophet Ibrahim got deformed with the passage of time and God corrected them in Quran and some, like circumcision, remains intact, so God doesn't felt the need of even mentioning in them Quran.
Brother Dawood your question "How come those elements become suspect…." expects from me to believe that current prayer, with more than 100 differences and numerous contradictions, is a ritual sanctioned by God not in Quran, but by virtue of its historicity. Sorry Dawood Bhai, for me Islam - Deen of Allah is 'completely' preserve in Quran and 'protected' by Allah.
Last direct question on this subject:
Had you not seen praying (Namaz) anybody, would you be to pray the same way you pray now?
If yes then guide me to that Ayats. If no then your religion lies outside of Quran also.