1. yes
2. yes
3. on the fence.

In regards to 3, what would happen if the 500K packs in presale were open to 3 minutes in a future release, and then 2M packs sell in that 3 minutes? While that is unlikely right at this moment and could be a fix in this specific example, it could cause problems down the line, where the presale promo card that would have had a run of 15,000, would then have a run of 60,000. In this case, it would be a 10% bump of ~1500 - but 4x'ing it makes the card far less valuable.

I don't have a solution for this, but I am leaning toward a hard cut off with all in the final block eligible.

However, since I like to go out on a limb...

How about a "preset" function for purchase packs, so the buy amounts can be set up prior to go live (perhaps in the last 10 minutes or something to stop automation if required), so then all that needs to be done is to click "buy" and it runs?