You can of course submit ideas for what your character can do/look like in Lyoko, but if it clearly doesn't fit your character's personality it's a no go for Tek. At least, that's what he said in the rules. Like, say, a fitting weapon for a farmer would be a scythe or something. 

And to answer your question of spots being open, Tek said the RP is always willing to accept. So just throw up an app, and he'll decide whether or not to accept it once he gets back.