Myrstery Plague

Yeah, I just find it better to play competitive with 60, however, the amount of mill that's in Standard means it might be safer to have a bigger deck? lol

I do actually agree with the getting rid of Red... except for Urabask, I need his 'all creatures you control have haste' ability for the mass production of Myr through Mirrorworks.

But you are right, I will probably get rid of Alloy Myr since Etched Monstrosity is removed and the majority of Red ... 😭(I get too attached to good home brew decks).

I have often questioned the need to go to the absolute minimum. I mean if I add one card to go from one-of to two-of then my odds go from 1/60 (or ~1.7%) to 2/61 (or ~3.2%). I've double my odds of drawing that card, while the odds of the rest of my cards went from say 4/60 (6.7%) to 4/61 (6.5%). That's 0.2% difference. Pretty minor, IMO.
Basically, I'd say keep the card count low, but if your deck wants 63 cards, do it. Don't be a slave to the routine.