Hello. I am a paper hoarder.
If I could, I would go vertical with my 12 x 12 as that is how I have my 8 x 10.
For now, I use a bunch of the clear storage containers you find at craft stores (see link).
Iris Storage Containers
I have them in a cart, labeled by color family. I have more holders than the 6 slots allotted in the cart, but those are organized by holiday. Even my SU and CM dp is separated by color family.
I am on a personal moratorium when it comes to buying paper until I can use the bulk of what I presently have. Probably should get back into scrapbooking to use it quicker!
Good Luck to you!