1) If you buy another docking station, be sure to buy an official one from Nintendo. Third party docks don't provide the correct voltage and can kill the console over time.
3) A second set of Joy-Cons is only useful if you expect to play multiplayer with four people regularly. Otherwise, the purchase of a Pro Controller is more sensible, especially if you intend to use the console a lot to play games on a TV. The Pro Controller is more comfortable to hold than Joy-Cons with or without a Joy-Con grip.
1) Besides, there have been stories of consoles bricking on third-party docks after certain updates, so, yeah, definitely not a very good idea. Then again, Nintendo charges an obscene price for those things.
3) I'd disagree about the Pro controller always being more comfortable than the Joy-Cons. I love the Joy-Cons for single-player games, they allow me to play in insanely comfortable positions - namely, in bed with covers on - that the Pro controller just wouldn't. When in "natural gaming position", though, yeah, Pro is always the way to go.
What more, let's see...
2) I don't know about a carrying case, but you definitely should consider a screen protector, that thing gets damaged easily. I was reckless enough to keep mine without one for over half a year and now I'm stuck with scratches forever.
4) I haven't played Pokémon Let's Go, but I did play the demo and it feels very much not worth the price in my opinion. Personally I'd wait for either a price drop, or just for Sword/Shield which are coming out later this year.
5) There is no Metroid game on the Switch, but there is Hollow Knight, which is amazing. If you haven't played it yet, I recommend you do.
6) As Rol said, try to hold out on buying an SD card for as long as you can because of price drops. If you can get to something like black friday, that'd be great for your wallet. But if you're not planning on buying digital games, there's a good chance you'll never need one. Personally, I buy digital only, and have been doing fine with a 128GB SanDisk card, but it will probably need upgrading at some point in the not-so-distant future.