Sheep

Correct. I used the ladder between routes 2 and 3 and it worked well enough.

I think it's inconsistent. Sometimes you'll be referred to as he, and sometimes they. Mainly because they works for all three options at a guess.

I think I've been hit once when I wasn't expecting to yeah.

Doesn't it need to be that specific Vanillite though?

You should be able to use the password "freemegaz" with a Data Chip at any PC. Then you can grab it from the Grand Hall.

Assuming Magician works in the same manner as Thief, then it's working as it should be already:

You need to use a Data Chip on one of the computers down there. I think that lets you access a second computer, which unlocks the way to the mega stone.

Grass/Ground and Grass/Rock are correct. You can find their PULSE readouts near where you fight them.

Yes, I think you just go find some more mirages.

No, once Flygon got Dragon Dance it got moved way back, the Chrysolia trade is now a 50/50 I think. Bruxish is one of the options, I'm not sure if there's another one because I got a Bruxish.

It can be found in the Wasteland caves as a wild encounter now.

I went up and down the ladder between Route 2 and Route 3.

There aren't any. Bug doesn't need one because it has approximately six billion pokemon obtainable before the first gym anyway. Dragon has Swablu and Noibat, though that seems like a rough time through Julia so it's possible you can get a third through the monodragon password, I've never tried it myself so I don't really know. Monorock enables an early Aron and Dwebble, though neither of these are obtained as your starter pokemon.

There's one in the cave near the Beryl cemetery.

I don't reckon. This is a game built on the mechanics of gen 7, and Incineroar didn't get Parting Shot until gen 8.