I'm also in the same boat wanting to mod my Wii for the Jap Smash but I got a couple of questions that still need to be answered before I dive in:
-Is Wiikey online friendly?(Will I be able to play Smash online using Wiikey or what about previous games, say I have Mario Strikers and I have Wiikey installed, will online work and be safe? And what about access to Virtual Console and other online channels?)
-Does it play all imports as long as there is not something like a SMG fiasco and what about backed up imports?
-Now say I'm done with my fill of the chip and Nintendo releases a firmware upgrade and I want to stop using the chip and upgrade and use the new official firmware, how does that work?
All online games at the moment work fine with modchips including the Wiikey. I can confirm this as I have a wiikey'd Wii and I've played Strikers online several times.
The Wiikey will play all import games so long as they are region-free. Not all Wii games can be played between regions.
The Wiikey will play any import games that any other modchip is able to.
If you want to remove the chip then you would either have to cut the wires to the chip or de-solder it from your Wii.