I'm from a late December server, so I had a little time to sit at lvl 70. I feel this is fair, since the older servers were basically beta testers for the game, very limited content, tons of bugs.
When I sat at lvl 70, I decided to build a stable of 6* toons. It costs less to go from 1* to 6* than to go from 6* to 7*. For newer players, you may want to follow the same plan, but stop at 5* instead of 6*. When your bench has sufficient depth, halt leveling and gearing until you have enough credits for the star promotions.
Farm cantina 6 and 7 for the best credit rewards. That's the best plan for maximizing credit usage atm.