I do agree most of Starhwats will be in the middle section (you can even see one Climatact's ends near Hancock), but imho they'll begin to spread from the far right side (Shanks' angle). Crocodile is in there too fighting Doffy and there's a fire leg which shoe doesn't really resemble Sanji's. If not for particular outfit, I claim for Ace in there. Also lightning above Moriah looks like Enel's doing.
By the way I don't think there's really a hero-villain side, more like protagonist on the first plane, but imho Straw Hats will occupy the rest of it). It looks like they goes for affinity, so we have Wanoeses first (Oden, Yamato, Hiyori, Kiku) along Kaido. After them the Totlandians (Katakuri, Purin and Reiju), so Dressrosa (Law, Rosinante, Bartolomeo) with Doflamingo linking to Warlords and affine (Perhona). Near Crocodile will probably be placed Buggy (as last Warlod) and Bonkure, along Vivi (above part of Straw Hats) and Ace, as Arabasta section. From Ace (so between Enel and some Straw Hat) Izo, Marco and Whitebeard, which will be split among the middle and right section. Near him, Roger, Rayleigh (Teach's angle) and Garp as tie to Marine section (Drake, Koby, Smoker, Tashigi and by WG extension, Lucci). Kuzan on the background near Teach's head. I can see Kid and Lucci clashing, maybe taking in Killer too as extra character. A little Carrot (as much as a Reiju) can appears in there along Woop Slap. Shirahoshi just emerging from the sea near the whole ship, which could happen to have Merry's polena.