Upakarmam and Purohita

What the purohita does is that he informs the day upakarma well in time distributes poonal etc and gives prior guidance.
The idea of performing upakarmam and vedarambham without a vadhyar is not envisaged at all.
If we are doing that presuming that we know how to do it ..that has no religious sanction.
The senior guru also performs upakarmam himself while guiding others and he performs vedarambham by leading the chant and performing vyasa/Kanda rishi pooja and Homam as per the shakhas and sutrams.
There is nothing odd about it.
If you are going to do upakarmam reading a piece of paper or book then you can do it the way you want..
but then you need not look either for jeaar or periyavaal or sannidhanam or brihaspathi swami or any shastri in the web..
Skipping the ritual seems to be better than doing vedarambham without a guru.
And after deciding to do vedarambham and upakarmam without a vadhyar or guru further questions are irrelevant

Yes, if you have respect for our traditions,  we should involve our Vadhyaar at least in Upakarmam.