...within the wider framework of the meaning 1, yes.Personally, I feel the numeral 1 was used to avoid ambiguity.
..again yes, Om [A U M] is made up of the 3, Brahma, Vishnu and Shiva. And, Baba Nanak wanted to depart from the traditional concept of OM to give it both independent existence and a quality [perfect]. But, where OM is sound [history: when all creation is at rest there is ONE sound, OM], Gur Ghar predicated it with Ek  Om [sound] kar [eternal]. Removed it completely from having attributes. Gur Ghar kept the ideology of the Brahm as the primary cause and through out Gurbani it has been epitomised.Professor Kahn Singh Nabha likens Oankar to Om.
..reference or source would be appreciated, if you cud !The full term is Ekankar Oankar. These two constituent terms are discussed separately in Gurbani. Ekankar is the nirgun aspect. Oankar is the sargun aspect. From Ekankar comes Oankar. Through the latter, creation is manifest, sustained and ultimately dissipated.
..mahalla 5, page 290 SGGSJIt is the Oankar that reverberates through everything as the Dunn, Anhaad Naad, Shabadh.
...naam, shabd, ikonkar, amrit, narinkar, akal purakh are not only synonmous but interchangeable in Sikh Theology. Naam Simran, in its literal meaning is simply, remembrance of God.Sat (Existence / Reality) encompasses both sides of the same coin (Ekankar and Oankar). This reality is its own name, not to be confused with Naam jap, which is but one aspect of Naam Simran.
...its an important observation because belief and knowledge are two distinct areas of rational reasoning where the former is wholly soley within the faith of the individual the latter, property of rationality and emperical experimentaion. For argument sake, one can ask for evidence of such phenonmena.We don't need to turn this into a faith vs knowledge debate.
...correct !Conceptualization of the terminology employed in the mool mantar serves to answer the question at hand:
...again, bang on ! But what to do when asked to communicate of the same to as many as possible people. Without language we'd struggle to exchange ideas or influence other people's behaviour. Human society as we know it would not exist. I'm mindful of the univesal message of Gurbani and the likes of HKJ and much more to have all, if not more rights to interpret the word of God through their own local dialect, caution must be had to its doctrinal and ideological significance. Of course, the difficulty in keeping the letter and the spirit of Gur Ghar intact is definitely challanging, but not impossible.Do the terms "deity" and "being" accurately describe the Divine in Sikh philosophy? My answer is no.
If Baba Nanak was asked about deity n being he'd probably dismiss it on account, "what isn't Waheguru ?".