Diddy has a link to a theme tutorial here:
http://gbatemp.net/topic/260327-wii-theme-team-creations/For channels, the reason you're getting different answers is that there are many different ways to do it.
Personally, I still use this:
http://gbatemp.net/topic/196912-wad-manager-15-multimod/I set it to use cios249 (although I guess any ios with trucha bug would work, but I can't guarantee it)
If a channel appears on the system menu then it's installed and it has no memory of how it got there. So if you can get it on the system menu then your method is as good as any.