I'd like some explicit mention of whether there are going to be new megas or not. It's fine with me if there are and also if there aren't, I just want to know whether there will be. I think it's odd they haven't been mentioned at all.
Team Meteor is from Reborn. The Eldest also wasn't taken out; Cera doesn't do anything to her regardless of your choice.
If you kept the Magma Stone: go to Kristiline and unthaw the TM shop to get Magma Drift, then enter Valor Mountain.
If you gave Cera the Magma Stone: I think you have to go to the villa first and explain what happened, and then go to the bottom of Crawli's gym where you'll find the alternate entrance to Valor Mountain.
She's in the sewers. If you've ever seen a set of doors down there that was locked (on the right side on the way to the switches that unlocked the door to the Garbage Crew), they're unlocked now.
Not currently. Maybe they'll be future sidequests. (although it doesn't look like there's anything noteworthy beyond the gear, unless there's a hidden item)
Luna does have Sableye. Also, Florinia has Ferrothorn at Fiore Mansion. (also if you're going to include Sun/Moon Pokemon it might be best to include a spoiler warning in the thread title)
Julia: Oricorio Pom Pom Style
Florinia: Chesnaught. Spiky moves in desert.
Corey: Salandit. Corrosion. Corrosive Field. Corey's name pun is corrode.
Shelly: Cutiefly
Shade: Dusknoir for reasons you listed, or Cofagrigus because of the eyes
Kiki: Mienshao
Aya: Scolipede
Serra: Alolan Ninetales
Noel: Drampa
Radomus: Alakazam
Luna: Absol. One belief Luna mentions a lot is that darkness is misunderstood. So is Absol. People think Absol cause natural disasters because they appear when they're about to happen, when Absol is actually trying to warn people.
Samson: Machamp.
Charlotte: Alolan Marowak
Terra: Dugtrio
Ciel: Crobat. You can't spell acrobat without Crobat.
Cal: Camerupt.
Blake: Cloyster (was actually his ace for a league season)
Bennett: Beautifly or Mothim are the only two butterflies/moths he hasn't used
Sigmund: Magnezone.
Victoria: Pangoro
Cain: Roserade
Fern: Amoonguss
"gender neutral"
"he"
Adrienn's pronoun is xe.
(not trying to be rude so sorry if it comes out that way, just noticed that it was acknowledged Adrienn is gender neutral while at the same time "he" was used to refer to xem)
The similarities between Titania and Erza are coincidental, and it drives Ame up the wall how similar they are.
Anyway, welcome to Reborn! Here's an ice cream sandwich
The badge is still in your case in the trainer card. It doesn't exist but it does at the same time. Tristan's badge raised the cap to 50 despite supposedly not being there, so I don't think we have to worry about his badge effecting the level cap.
(it's also possible we grabbed one of the badges from his house when we go there)
It's in the house with the door where the guy says he's never been able to open it. You need 2 keys to unlock it. One of them is in a cave near the top of Silver Rise that's inaccessible during your first visit with Tristan (it's near the staircase that goes to/from the peak) and the other is in Shade Forest. In Shade Forest, there's an ice pyramid with a staircase being blocked by some boulders. You need to go around activating crystals (same as in Silver Rise) until everything in the way has been removed and you can go down the staircase. There's also a catchable level 45 Froslass down there.
I haven't played 3.1 so I don't know if her team changed along with the new ship scene, but in the original release of episode 3 she had Crobat, Cacturne, Milotic, Blaziken, Zangoose, and another Pokemon that I don't remember but it wasn't Nidoking.