When I buy things in the store do they apply to all of my characters accountwide or is it individually?

That differs from item to item. It's usually in the description.

Costumes, ships, and emotes are account wide. Slots (Ships, Inventory, etc) and Boffs are for one character only.

Except for costume slots, those are account wide.

Costume slots are the only slots that are unlocked for the account not for one character. Bridge Officer slots, Ship Slots, inventory slots, and bank slots are all unlocked for only one character.