Current fleet it bad yes
#Fleet Help
frosty acorn
not that good but showing your dock will help assess options
frank thicket
Dock
frosty acorn
Well first thing I would advise is going to the Guild Shop and get Unicorn
Unicorn is one of the most useful ships in the game and the fact she's that easily accessible makes her just way too good to pass on
So I personally would replace Bismarck for her in that case
Then replace Yukikaze with Portland and make Portland most left unit of your frontline
And then after that, limit break (giving them bulins/purins) your ships so that they'll be better
So I would go:
Nagato/Unicorn/Enterprise
Portland/Laffey/Swiftsure Helena
Give 
priority to Enterprise and Nagato
frank thicket
Is there some lvl after which i should start limit break
frosty acorn
do it immediately after 10/30/70
frank thicket
Alr thx
frosty acorn
Early on you wanna focus on one fleet first because you won't have the resources to have 2 strong fleets.
When you reach World 9 then you consider using a 2nd fleet and hopefully by then you can have access to more strong ships
frank thicket
What should be the criteria to choose ships since rarity doesn't work
frosty acorn
Well you can loosely consult a tier list or ask in help channels
https://slaimuda.github.io/ectl/#/home this tier list is fine most of the time minus some questionable decisions at the DDs section but it's good enough for a loose reference
But one thing i can guarantee is that Enterprise and Unicorn can be used for the entirety of the game so that's how strong they are
frank thicket
I see, also should I immediately Max lvl the skills of nagato and enterprise as priority if I have resources
frosty acorn
Oh right and also buy Helena from the Guild Shop. Put her in the Dorm as well. She'll be good for your 2nd fleet when you specialise that fleet to kill bosses.
Enterprise > Unicorn > Nagato imo
Well Enterprise first is great because she only has 1 skill to raise albeit an amazing one 
oh and reason why i've kinda ignored saying anything of priority for Swiftsure is that you're more likely to find someone better than her. Not exactly worth giving 4 to
Honestly just put Helena in for her
Oh yeah one more thing, don't forget to also use that level 8 and level 7 
to limit break your ships too
frosty acorn
Oh sorry this is really one last thing but when you're in Unicorn's profile page you will notice a Retrofit tab on the left side. They're basically an upgrade to the ship (well minus maybe 1 or 2) Do that when she's high enough level to get the Modernization node in there. Her retrofit is amazing and the preload she gets from it is what makes her the best healer in the game. Helena has one too but isn't that high a priority to use your resources on