Mounts, pets and costumes can be used by all characters as long as they're on the same server. If you've got some EU characters and some NA then they aren't able to share collections (or anything else).
Consumable items are 1 use each. You can give them to different characters, for example if you buy a motif pack you can give each motif to a different character, but each one can only be used by one character, the rest will need their own copy.
Just as a note, don't get too hung up on motifs. Yes, they are cool, but they offer nothing in terms of mechanical benefits. If you're persistent, you'll find them. It may be slow, but it's possible. And even after that, you'll have a player market selling them. They typically don't get too expensive. I'm not sure how prices will go on the consoles though.