I wouldn't use Solder Wick, because it's known to rip traces of the board. You should use flux instead. You can also get the case form jlcpcb(I heard that they are cheaper)
Yes it's possible use omgwtf for reference and look at the RVK-01 Compendium (https://bitbuilt.net/forums/index.php?threads/wii-rvk-01-compendium-released.93/). There you can look at the av traces and work out a trimming line
It's 6-layer so you might need to sand the edges a little bit more and at an angle (you should be able to slightly tell the difference between the layers)
You don't have to model the GC controller your self. There's a scan of it on the Forums, but if you're working with a scan you have to use a mesh editing program(like blender)