Regarding mechiras chametz- I have no problem with anyone or any community that wants to be super machmir and not rely on mechira, of chametz gamur or personal chametz. To each their own.  Rabbi Yudel Shain is known as a super machmir person and that is fine. But he was not talking chumra but what is allowed and what is not allowed. The shulchan aruch says mechiras chametz works even though it is haarama. I dont know where he gets this obligation of the mechira being blev gamur as an absolute condition.. At least it should be stated as a chumra, as a lechatchila, etc. I know many who dont sell chametz gamur such as bread and pasta but will sell whisky because it is expensive. This fellow with the challa from the Rebbe, clearly that is something super valuable to him and should be allowed to sell it even lechatchila except by the most machmir. it doesnt seem like a stretch to find this fellow a reasonable hetter.

Regarding kiddush or sheva brachos and a mashgiach-

Maybe I am missing the metzius and need some background. I am 49 years old, grew up in a frum home, davened in frum shuls my entire life, learned in frum yeshivas... I dont think I have ever seen or heard of a mashgiach at a shul kiddush. I have no idea what he is even talking about and who thinks this is something required. Ther person, a frum person, in the shul in charge of the kiddush buys food from a kosher caterer/shop or has someone in the shul prepare it (often a combination of the two) and then puts the kiddush together. I dont know what this demand for a mashgiach is about. Is there anywhere that does this regularly? Lakewood? I know of a shul that "rented" out its kitchen and hall to a caterer (someone from within the shul who had a catering business) and the caterer had to have a mashgiach (which was someone from the shul, not an official mashgiach). ANy event, including a shul kiddush, that the caterer catered had to have a mashgiach, but that is because the shul wasnt preparing it but a caterer was doing it "externally". This was an uncommon situation, not the norm. Most shuls I am aware of  do not have such an arrangement for its kiddushin.

If I make a sheva brachos for my relatives I need to have a mashgiach? What kind of narishkeit is this? is he talking about where I rent an event hall with a caterer and have it held there? Then, sure - the caterer and hall should have a mashgiach. But if I make food or buy food from a kosher caterer and put together a sheva brachos, and even if I hire waiters to serve the food, I have to employ a mashgiach?

Am I missing something in the metzius?