Want to purchase the legion but want a certain outfit.
No, you would have to buy the killer and the outfit separately. You can purchase cosmetics for a character before buying the character themselves, but you won't be able to use the outfit until after you have unlocked the character.
Nah mate, you gotta bye the character first before your able to use the outfit. I guess it helps when choosing out of 5 killers or so with outfits already bought