it all depends on the teams You want to run.
STR team:
Focus on getting G2 Luffy. Level Arlong, Alvida, and Mr. 5 and Usopp. This will be your team for Mihawk. You'll need 0-5 gems (based on orb luck and levels). if you're going for 40 stamina.
Slasher Team:
Tashigi, Kuro, Arlong, Zoro and a Utility character. Most likely Usopp.
Int team.
Towel Nami, Buggy, Gaimon (switch for chopper later), Siam, Usopp.
Decide the group you want to concentrate on. Then work on the Captain of each squad (G2 Luffy, Arlong, Towel Nami). Get that Captain to about 70 then work on getting the others to 50, 60, 65, 70. Do it this way only if you want advice to follow.
Since we are getting Red Turtles for the next 2 weeks I'd focus on your STR team. Get Luffy to G2 then to Level 50, then evolve Alvida and get her to 50. You can use your turtles from turtle time and the Arlongs you drop during the event on Arlong. Mr. 5 can get baby turtles, if you want to evolve him as well go for it.
If you don't care for a STR team just focus on your Slasher team.