Topic name. Sorry if this has been asked before, I couldn't find a forum search feature.

Essentially I'd like to know if there's a way to filter for this, so I can know how many new copies of cards I need to buy when building decks. If it exists, is it also possible to filter in other ways, such as when the copies in decks and inventory is equal, or if there are one or more extra copies of a card in inventory?

Yes, in Inventory -> Filter -> Add more Filters -> Count in Collection -> Unused count