Which characters are playable in the "base" game?

[Shoah Kahn]

Are the playable characters all present and accounted for -- Ms. Freeze, Deathstroke etc. -- irrespective of "base" of "deluxe" purchase, or are only the four initial characters playable without addition investment...?

(thanks)

[Bunny Massacre]

The 4 main ones. Then you beat the story, and you can pick an episode, do missions there, and unlock that character. I unlocked Deathstroke in a few hours today, probably 4? I wasn't really after him, I just want to play Harley, so I didn't go hard. Still didn't take very long. Story took a while, maybe. Mostly because I did every single side mission for gear. You could probably just put it on easy and run right through it though.

[Shoah Kahn]

^ So, to play as the DLC characters, you need to:
1. Beat the game with the base game squad
2. Play some DLC missions (with the four main chars.), until you unlock the DLC ones

...Correct? If so, is it made which missions must be beat in order unlock a given character? Also, are save files transferable in this -- so as too (for example) load up a game that already has the main story completed?