A helpful thing to remember is what the different errors mean:
If you try to install a WAD but you get a WAD install error, then the WAD was messed up by Freethewads (either as a fluke or you can't use Freethewads on it without using the PPF first).
If you try to play an installed WAD but you get a black screen, the region is not compatible with yours. Trying patching it with Freethewads. If you already ran Freethewads, then it just doesn't work.
If you try to play an installed WAD but it resets your Wii, you need to update your firmware to the latest version of 3.2 (March 20 version).
If you try to install a WAD but you get a WAD install error, then the WAD was messed up by Freethewads (either as a fluke or you can't use Freethewads on it without using the PPF first).
If you try to play an installed WAD but you get a black screen, the region is not compatible with yours. Trying patching it with Freethewads. If you already ran Freethewads, then it just doesn't work.
If you try to play an installed WAD but it resets your Wii, you need to update your firmware to the latest version of 3.2 (March 20 version).