Just do whatever your first playthrough of Nier, collecting the weapons doesn't matter as you have 2 other playthroughs to be able to get them, follow
this guide on your second or third playthrough to get all the weapons, then for the third playthrough save before the point of no return, pick top option for ending C, then reload immediately if you want to do ending D right away (need to complete the last area again, but it's not that long.) but if you want the platinum trophy save ending D for after.
Also Nier is really easy, even with some of the ridiculous bullet patterns near the end of the game because you can just power right through them. you keep all your weapons for each playthrough too so you have phoenix spear right away. this is the one weapon i do recommend saving for in your first playthrough because it kills everything in 2-3 hits and bosses in like 5 even unupgraded
