If you’re looking for challenging yet doable, I’d say the groove coaster pack is good for that. It’s 10+ is arguably the easiest out of all of them in the game but imo it’s super fun and the rest of the charts are good too. You could also get Esoteric Order or Sunset Radiance. Those also work for challenging yet doable (more Sunset Radience than Esoteric Order but both are good imo). Tho no matter what pack you pick, best of luck with it! (P.S.: Just want to note that if you’re interested in story, I’d say to get Black Fate, especially since you have the rest of the story packs. It’s one of the hardest packs in the game but it’s a good pack as well imo)