You can play Kludge and ignore the others but these games are rich in lore so you will miss hundreds of small things, not anything related to the main story though...
You can use this link for a korean wiki for the white feather locations
Tjuerma 2 is always accessible once you unlock it, you go there by going to the garbage dump you were spat out at the beginning of the game
Idk exactly what quest that is, if you can send an image of the event list I can give you a save
I wish there was some sort of recap of the more important stuff since these games are so packed with content that even replaying them you are still likely to miss a detail of the lore.
Big nuke with Yolnaya using Wild Life + Charge + High Fury while equipped with whatever part makes your elementless attacks the element the mechagod is weak against and whatever equipment gives you the higher attack (two Plamia Hearts, strongest weapon...).
I have grinded the three mechs (plamia, chromea and zemlia) so much I have everyone penultimate weapons, four machinarc scit and four mashinarc dusha and both plamia hearts on yolnaya as well as all the element changing parts
With 2 Chromea Hearts and AGI boosting parts (including the Steelen Wind one you got from its weakened version) Dita should be able to outspeed it in order to bind it.
