Short answer: tackle the event best you can for at least a few days, but bail if you just absolutely cannot progress. Event-exclusive ship girls, especially European ones, are for the most part worth it, but burning all your resources for no return is not.

Long answer: ship girls being levels 40-60 is actually not that bad for tackling an event on casual; you're around the same level that I was for my first event. Getting those event-exclusive drops is just as important as equipment and leveling your characters for clearing future events - for example, the boss you're fighting can drop Littorio, who at level 1 will outperform a maxed-out Kongou Kai Ni on this map; she can also drop Zara who is just as useful, among other very good drops this map.

Besides this, even if you keep failing to kill the boss, I find tackling events will net you a decent (not great, but decent) amount of experience regardless, even if you're only scoring A-ranks, so your ship girls will still gradually level up as you keep trying, killing two birds with one stone. Keep in mind that getting stuck on Last Dance is normal for pretty much anyone at various points during these events, and it all boils down to RNG in the end, so try to have patience if you find yourself unable to finish off the boss very quickly.

But, as a general rule of thumb, even though you should try to get some event-exclusive ships if at all possible, if you keep at it for a little while and you're just completely stonewalled, there is a point at which you should call it quits before you burn all of your precious resources. After all, if it becomes clear that it's going to accomplish nothing, you shouldn't waste them for no reason.

Either way, you can keep an eye on information as it comes out and keep at it if desired, but to start, let me give you what I used to tackle phase 1 of the first map (you probably won't have any historical ship bonuses like I did, but you should still be able to clear without it, with some effort).

My comp was FBB - CA - CL - DD - DD - CV, which will route C->F->H->J. Use spoon (vanguard) formation for the preboss nodes (C and H), then line ahead for the boss node.

Equipment-wise, for the FBB just have the standard 2 large guns, 1 scout plane, and a Type 91 AP shell if you have it, a surface radar if you don't. CA should be 2 medium guns, best you have, 1 scout plane, and a Type 3 shell if you have it, radar if you don't. CL should have roughly the same loadout as the CA except go with a slightly smaller caliber for accuracy (i.e. CA will be 20.3 cm, CL will be 15.5 cm if you have it or 14 cm if you don't), and a radar. The 2 DD's should either use 2 small caliber guns and a radar, or a TCI setup if they're invariably failing to punch past its armor in night battle (either 3 torpedoes or 2 torpedoes and main gun/radar/whatever). The CV should just be equipped with the 4 best bombers you have to take out as much of the fodder ships as possible - as long as at least one has AA stats (torpedo bombers), you'll automatically get AS+ since the boss has no air power in casual.

I'm assuming you don't have any proper planes for LBAS yet, nor the resources to spare trying to get some, but in the off chance you do, remember to send them all to the boss node and not on anything else. At that point just hope you get a lucky snipe on the boss - largely relying on a good night battle for this - then keep farming the same boss node afterwards until you get some sweet Italian ship drops. Once you do - you're in business.

Have Anti-Installation ?

Have Daihatsu or Drum?

No have LBAS but you have Ryuusei or Tomonaga?

Have Skilled Lookout?

Have Renpu?

Have Night Recon ?

If you have all of those, just DO IT!