Nothing wrong with a well mannered question.
Tournaments can be two things; An event ether held my the Game-masters by a clan, these normally show up in the event section of the forums and happen at a particular date and time. The other kind are the tournament severs that run pretty much 24/7. While the prizes are a lot smaller this can be a nice way to rake in some TC, assuming you win of course. The system used prevents anyone joining during the tournament, after all its a knockout system. When the sever says the current tournament is over you will have a few minutes to join it using the /enter (or /en for short) command.
The weapons you have seen are very much accessible, you just need to load the mod for it, while in single player (or multilayer, if you are an operator) and press and hold Ctrl + m (for windows, mac I think is function + m) and it should bring up a list of all the mods you have, the game already comes with a large variety of them so have fun exploring them.
When you buy a texture item you can active it in the Deactivated items section in the shop tab. When you have bought one you can upload an image which will be displayed on your Tori while you're in-game, the size of the image will depend on what sized texture item you have bought.
You can create an image yourself or buy one via commission from an artist here on the forum. You seem intelligent enough to know about plagiarism but I feel the need to anyway.