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.
6) Micro SD cards should only be purchased from reliable manufacturers such as Samsung and SanDisk. If you prefer to buy games physically, you won't need a micro SD card for a while because save games only need 10-100MB in the majority of cases. Prices for micro SD cards keep dropping over time, so managing to hold out literally pays off.