No it will just be in Ur download list and just click download and the vita version is in the download list too
The pre-order costumes are definitely in the form of a code
Not always. I purchased LittleBigPlanet on the Vita at launch off the PSN and the costume packs were waiting for me in my download list.
So if you purhcase the game digitally, on either PS3 or Vita, then you will definitely automatically download the costumes.
For physical copies it may be an extra code inside the box or part of the online-pass code.
Yea how do you get the bonus
You will get the code for the pre-order costumes on your receipt when you pick up the game at any store outside of PSN. It won't be in the case or manual or anything like that because then otherwise, anyone will be able to get it without pre-ordering the game.