After I evolved my Feebas, I took on the league, and had no extraordinary troubles with any of the E4 or Hau. Afterward, I fought Hala in Iki town, and his team was rather inflated in levels. I wasn't expecting that, but I triumphed regardless. Hala gave me the Z-crystals for the other two starters, and I headed up Mahalo Trail where I bumped into Lillie and Nebby--or rather, fully-evolved Nebby, aka Lunala--and immediately noped out. I poked around the game for a bit, battling any trainers I missed along all the routes I'd been to, and taking a few photos at the Photo Club thing. Nabbed a goodie of my Dusk Mane Necrozma acting all intense and stuff. The Photo Club thing is actually kinda fun, once you figure out how it works.
When I felt I was ready to advance the post-game story, I went and caught the two Stakatakas that were roaming Poni Grove. Then, I started the RR episode by going with Sophocles to Festival Plaza, and crushing the RR grunt with some actually-decent Agency rentals. I noped out of doing the Aether Paradise section for now, instead focusing on exploring the post-game parts of Poni Island, making it to Resolution Cave and the Battle Tree. I battled Red's OP team, noped out of the Zygarde encounter, and tried to evolve my event Rockruff. Sadly, since I'm playing UM instead of US, I have to wait until 5 AM to evolve it. I'm not awake at 5 AM, this is Tauros-puckey...
EDIT: Apparently, I could have evolved my Rockruff if I'd gone to the Reverse World... I guess that's my mission for tomorrow, then.