1.DEX/AGI/STR
Yeah I just played for that long in the post-game for my first slot, to get 4k in all stats you would need from absolute zero, about 80 ancient metal pieces not counting any wellness passive bonus and workouts, since you can do infinite dungeons runs per week currently, but only train with mr white once, I just had to get a bunch of metal pieces and train with him while killing the kobolds at starting area to replenish the absurd mood loss, and even then I'm not counting the most absurd bonus with custodian strength, which snowballs your stats with the lvl% things, causing your power to really get out of hand.
And all of this can get even faster if you are not doing a "clean" run! Which means having no mutations at all, if you allow mutations then you can just abuse the sovient bunker syringe and gain even more stats on top of the training stats. I was not sure what the consequences of mutations would have in the future but for my first character I wanted to keep it "pure" as much as possible for the first slot.
2. Swordmanship/Weapon Training Overall
Ghouls + Warrior perk is 12k weapon exp per kill if solo, and if you are as strong as I was when I started fighting them, you will be one shotting them every time. And they also respawn by changing maps which makes farming them very quick and you can become a saint of your weapon very quickly through them.
3. Custodians/Lore
Probably my favorite late game thing, almost an extension of my fascination with the church, Zacharias obviously either tampered with Ichor really damn hard or he is also a Custodian himself judging by the blood stone ritual, Mr. White also being a Custodian, whoever killed the tutorial NPC and also the Custodian who invaded the kobold hideout in the leader diary. These guys are clearly up to the shadiest stuff in all of Sinathir, and Zacharias might be just about the weakest of them all right now, while being leagues above any other NPC you can recruit.
Also the way Mr. White calls you Zacharias' thrall makes me think joining the church might have not been the greatest idea in hindsight!
Also the attention to detail in this game is nothing short of amazing! Meeting Mr. White with certain companions creates different reactions, unlocking even a stern talk with Suong. Zacharias just nodding to the man calmly is very in-character of him though. My next goal is getting 20 Quentin White kills to get his full diary entry.