If I pre-order the physical + digital bundle for Bigby's on dndstore.wizards.com, will I receive the pre-order items (frames, backgrounds, etc.) that D&D Beyond typically gives out for digital pre-orders?

while they haven't announced specific pre-order incentives for Bigby's, if and when they do, your pre-order code for Bigby's will include them.

I haven't ordered a pre-order bundle yet. Is the code provided when you pre-order the bundle at dndstore.wizards.com? And then you come back here and redeem the code?

no, the code is emailed to you in the same manner as if you were buying a gift on DNDB.   Whomever claims the code gets the book.