It is a spinoff
It's not a game with gyms or trials
There's an elite 4 but you have to so some tasks instead of fighting them
There are fights but most of them are scripted or are pretty straightforward
It's like a semi-open world interactive adventure, idk how to describe it, it's kinda boring unless you are really into pokemon
And the pokemon go integration is minimal, you can hatch your eggs and get candy in the switch game without having to walk irl, you can also register (not catch) some rare pokemons on the dex with the switch game dex
They will also release all of gen 4 on go at the same time as the switch release
Both games are different, one is more fight centered, the other is more mini game and story centered, the eevee one is the one about fighting (not sure)
Also you dont choose a starter, it depends on the version
Nothing BIG, pretty sure they will reveal ONE gen 8 pokemon on the game itself, the things from the other leaks are MOSTLY true, no hms, it's on kanto bla bla.
Gen 8 will not release this year because if it somehow does release this year it will be shit, or atleast that's what i think, i have not actually seen the development of the gen 8 games.
Extra stuff:
>People at e3 will be able to play the new smash game
>Bunch of teasers with no dates for animal crossing, star fox, another zelda game, another mario game and a lot of third party stuff.
>Fornite announced and released on the same day as the nintendo e3 presentation starts, get a big sd card JUST FOR THIS ONLY GAME
>One fire emblem game announced and scheduled for this year, another one teased for later
>Mario kart for mobile teased

Dont expect much, this year it's gonna be full on pandering to smashfags and some other big franchises like metroid and such (but not as much as smash)
Also pay a lot of attention to the movesets of smash characters since they mirror mechanics from their upcoming games.
Also price drop and virtual console with a new name
All old consoles gc and wii too.