DarkCorp is a softmod that allows you to run disc backups (burned games) from the disc channel, without having to use something like NeoGamma. However, it doesn't play well with other apps, and can cause bricks. You can't even use it on newer Wii's. There is a reason it is often called "DarkCrap." I strongly suggest that you don't install it. For more info, go here:
3) is there some more detailed description of optional darkcorp mod? Have I understood it correctly that it will enable me to place all my original games backups from usb hdd as separate channels so I could launch them from the wii menu without the need of launching usb loader?