Any idea of bitmain batches size?
No - and the source code from Bitmain's listing page doesn't have the remaining count listed (yet).
Are you saying that the hard cap is viewable in the source of the page during the sale?
Sometimes - yes. I am usually scrambling to purchase before they sell out, so I'm rarely looking at the page's source code at the times that it shows the remaining count. It does show the max order per person = 1 this time, which I've confirmed by attempting to add more than 1 to the cart.