not every one of them. If the developer accepts the mod it's legal (E.G. DoTa for Warcraft III: reign of chaos)
No
No it is not illegal.
Yes
no
Yes...
you can always go for a alienware computer as they are designed for gaming
No they arn't illegal. You can't get arrested for having them, but expect to get banned on Xbox Live for having them.
No, it is not. However, it will probably not work on multiplayer servers unless this mutant mod you are talking about is a client-side mod, which is like a hack client, and would not be allowed on most multiplayer servers. If you are talking about mutant mods as "illegal by Mojang", then no.
gaming commission
No, Minecraft Forge is not illegal! That is why many people still use mods.
Modding any Xbox hardware is illegal and should not be done.
To get mods you would have to JTAG your xbox which Microsoft will find illegal since you can pirate all types of material and you will probably be caught and banned if you have xboxlive.