1. Maybe it´s also stupid, but why don´t you use Fraying Sanity?
... Because I misread the card. I thought it would only trigger in your opponents turn (which would be nonsense, because you have very few ways to mill many cards at instant speed).
Since Jace is pretty expensive (both money and mana wise), you could drop him for
Fraying Sanity.
2. I know this card is very strong, but are there any cheper alternatives for Visions of Beyond? 😅
Afaik there is no card that does the same. You could do something like
Frantic Inventory or at least
Mental Note.
Oh and you could add some
Evolving Wilds as well, because they trigger your crabs twice.
Overall I think you are free to swap some of the mill spells around depending on what you like most.