Who should I lvl??? and any other advices please

Hey guys,
I am struggling with couple event isles and I do feel like I am spreading my teams too thin across the characters.
The team I usually use is

G3 Luffy
Arlong
Asura Zoro
Kuro
GP Usopp
with friend Arlong or G3 Luffy

I think I will use my vivi with for upcoming Mihawk and try double G3 team after I have secured Mihawk.

Anyways, as you may have guessed, I am trying to focus on evolving my characters - mainly fine tempo nami to towel nami, Izo and Jozu and Alvida. Since lvling to max have already cost me about three turtle time events, I think to max all of them I need 2 more weeks, plus raising them to decent level so they are actually useful.

I think that will definitely bring some fun as I can then utilize various teams, but all my friend captain are at relative higher lvl than I am.
For instance, I barely beat Buggy and Arlong expert and dare not farm on those isles.

So any advice for me to beat other upcoming isles swimmingly or characters I should prioritize on? Thanks so much in advance!!!

Yeah, it can be pretty difficult deciding who to level up, but focus on one main team and level those guys up until you're comfortable with their stats.
When dealing with event isles, you need to consider the boss you're dealing with. For instance, Arlong is a STR character, so naturally a QCK team would be better suited for him; However, using Gear 3 Luffy and having a Gear 3 Luffy Friend is always a very powerful route, especially if you include a bunch of QCK characters too.
In my opinion, you should level up your INT characters and focus on an INT team UNLESS you are sure you can get Mihawk and his 2.5 boost will make your slasher team very strong. I hope I helped.

Yeah, it can be pretty difficult deciding who to level up, but focus on one main team and level those guys up until you're comfortable with their stats.
When dealing with event isles, you need to consider the boss you're dealing with. For instance, Arlong is a STR character, so naturally a QCK team would be better suited for him; However, using Gear 3 Luffy and having a Gear 3 Luffy Friend is always a very powerful route, especially if you include a bunch of QCK characters too.
In my opinion, you should level up your INT characters and focus on an INT team UNLESS you are sure you can get Mihawk and his 2.5 boost will make your slasher team very strong. I hope I helped.

You have a ton of characters, damn. Honestly just focus your team based upon the weakness of whichever boss you are facing. For general story play I would run that team you listed as that is a pretty solid team. Odds are your main problem with 30 stamina islands is that you aren't stalling out so all your specials are up before fighting the biggy at end. Also for reference buggy is a pain in the ass for g3 luffy since you want to pile all your hits on a single target and his minions screw with that.

For Krieg the only change I would do is swap kuro with Mr. 2 4* (important thing to keep in mind is that you deal double damage to units so take that into account when min/maxing your team). You should always go with double g3 luffy over g3/arlong as g3 luffy and gp usopp don't get the slasher buff.

Another option (for non-mihawk events) is to evolve your fine tempo nami to towel and run an int team as you legit have all the key parts to a bitching team.

That team would wind up being:

Towel Nami (captain 2x)
Nico Robin
Buggy the Clown
Brain Point Chopper
GP Usopp

This team has a crazy ass burst with the specials which is generally pretty solid for all non-raid event isles (with the exception of garp if I had to guess). There are also a bunch of crazy good int chars in the future that you can mix and match in.

Edit: And yeah you can also run a slasher team with mihawk after zombieing him.