Not only will you be able to go to your local store to buy the game, the PSN will also be selling it as a Day 1 digital title, complete with the pre-order costumes. And, as expected, if you download the PS3 version, you’ll also be able to download it on your PlayStation Vita.
As for just how much single player content will be included, Seth had this to say:
Beyond arcade mode with intros, endings, and rival cut-scenes for every character and all the multiplayer stuff, All-Stars has tons of interesting challenges and trials (both overall trials and character-specific stuff). Certainly it’s hundreds of hours of content there, and a very extensive set of unlocks, from titles, to taunts, to character-specific intro and outro moves, musical themes, badges, etc. Hope this helps.