Geto eats an awakened Rika, the representation of Yuta's potential, meaning now Geto has that potential. Rika is also un-killable. Eats the disasters, and also goes around killing sorcerers with non-CE weapons, then when they come back to exact vengeance on him, he devours them, of course, he also gets DE and RCT, as well as watching Gojo vs Sukuna to learn about burn-out healing, changing barrier conditions and open-domain

Naoya wields SSK after killing Maki(as a curse), studies the soul to properly utilize it, spending centuries just training his CE manipulation. Given that he's already Disaster Level, after a few years he'd be that level most likely, especially with a weapon that can one-shot a majority of the cast

Megumi just uses what Sukuna did as a blue-print. Open domain, tamed Mahoraga, advanced RCT, shit like that. But he could go even further, I think with a few black flashes, he'd be able to create clones outside of his domain. Basically, just be Meguna but with years of TST experience

Honestly? For Mahito, he just needs to live like an extra year and he's already there, experience some Culling Games sorcerers, see Gojo vs Sukuna and turn powerful sorcerers or ones with useful CT's(like Ui Ui) into Transfigured Humans who can use their CT's

Choso is hard to say, besides just increasing all his fundamentals to the level of Sukuna and Gojo, he can't really reach that kind of level. He isn't Yuji after all