What/who should I focus on?

   Thanks

Got a nice start of a DEX team

Zoro,Law,Apoo,Smoker and Doublefinger.

Zoro - great captain
Law and Apoo work really nicely together so level up both.

Smoker and Doublefinger less important but still work well with the others.

Most of your other units aren't worth the effort till you get better units but I guess you could focus on Jinbe, Nami version 2 and Killer.

First at all, try to get some Golden Pound Usopp skillbooks (in the duck fortnight) and save them until a double skill up event comes
Second, dont level up Laboon, he can be your chance to get Mihawk (if he comes back)

Your best captains are Fine Tempo Nami (later Towel Nami gives you 2.5x ATK for INT), Law, Jimbey (Zeff has same captain ability, but his stats arent so good), Zoro and Killer
crewmembers are always difficult, but I think useful are these: Luffy (evolve him to Gear 2), Smoker, Apoo, Impact Usopp, Mirage Nami, Mr 3 (after evolve) and Curiel

It is really difficult, because there arent often Jimbey oder Zeff friends, otherwise you can build a good fighter team
Also you can build a really good DEX team, I think Zoro captain with Law, Apoo, Smoker and Golden Pound Usopp. But also here, I dont know how many of your friends use a Zoro as captain
I would focus on this two team, and try to get Arlong, he is a really good crew member (second highest ATK from all global units) and also his captain ability 2x ATK for Slasher is useful
Also Sir Crocodile is a really strong unit, try to farm him and evolve him to his second form