Any advice for new player entering endgame?

I just started playing this game about a week ago and I’m entering endgame now, but am kinda overwhelmed by all the build stuff. I’m looking up character builds and seeing them talk about arche tuning, weapon cores, sigma sectors and all that and feel kinda lost. I would greatly appreciate if anyone could give any tips or pointers for what I should focus on first and what to do later.

When I say entering endgame, I mean I literally haven’t done any story progression after finishing the main story, not even the first hard mode colossus. Since then I’ve just painstakingly grinded my ass off to unlock Ultimate Bunny, Ultimate Valby, and Ultimate Freyna. I’m just about to get Bunny in two hours as of the time of writing this, while Valby and Freyna are still gonna be crafting for the next 2 days.