Using my 2nd character slot, I get a new mag too right?

[Ludamec]

As in I have to do all quests over again, so I do get a new mag? Also storage is still shared by all my characters too right?

[Xaeris]

Yes, you'll get a fresh mag.

[UnLucky]

Yeah you keep your storage (meseta included), but everything else is brand spanking new.

Have to unlock all the areas, COs, classes, difficulties, and level caps.

Mags are per character, so you can't swap them across your account. You do get a new one though, just like on a new account.