You get armor every 5 honors you unlock (which also unlock XBox achievements) up to 30. The 30 achievement armor isn't all that great or numerous, however. There are a lot of really easy achievements you can do to get up to 10 or 15. The 25 achievement stuff is pretty awesome, though. Here's a list of achievements anyone can do (almost all achievements do not count in local versus mode):
Watch the intro movie. (Exit out of the game, start it, let the move play and press start the first time it asks you to.)
Create a character from scratch.
Modify an existing character
Create a character with 4 skills using all their skill points (easiest to do with low level skills)
Complete story mode with Yoda
Complete story mode on normal (I assume you can get both of these on the same run)
Maximize a style's level (just play the same character 'till their style is at level 9)
Get Soul Calibur (Final form) (Play through story with Sigfried to unlock it, then buy it in character creation)
Get Soul Edge (Final form) (Same but with Nightmare)
Beat Arcade mode

That's 10 achievements without much work.