Yes, there are 5 total cargo hold tabs. You can unlock them (account wide) for 1050 cartel coins each tab (times 4, tabs 2-5). The (account wide) unlock is (account wide) not (legacy wide), it will be unlocked on every current and future character on your account, even on different servers. This is also the same for the (account wide) inventory bar unlocks.
So, for 4200 Cartel coins you can have all 5 tabs (including the initial free one) unlocked for all of your characters on that account.
This ^^^ its worth the cartel coins. And it works even on the PTS server as well.