Wii Sports Resort is a heavily competed game. The Wii U gives you a huge advantage, but not every top runner uses it. Loads and lag are reduced compared to original Wii.
32GB is the fastest. 32GB > 8GB > Wii. Japanese is the cheapest. You can buy a Japanese Wii U and make a gaijin Mii. This will change everything, including Wii games. If you prefer Japanese, you won't have to. You can change the game to Wii Mode, but don't. Just get used to the higher speed of the Wii U. Unless you want to change from HD to SD, you won't need the GamePad if the Wii U is used and you are only using it for physical Wii games. Using a Wii U in Wii runs should be as common as PS2s in PS1 games. Go for it!
In the past, runs below a certain threshold could be submitted without video. Now, this system has been removed. All runs require video proof from now on.