hmm steam + electrics probably wont go well together no. If you did take it to nissan they would plug it in to diagnostics (cost prob £90) and find out where the fault code is, if there is one.
to me it sounds like either a module is faulty or a connector is shorting. Due to the range of things that dont work it could be the BCM that has been steamed? it i located alongside the accelerator pedal and has about 9 different connectors going into it. right next to the carpet in the driver footwell. its a bit of a fight but you could take the module out and inspect it for any water/moisture, if you find it i would go at it with a hair drier immidiately befroe it all corrodes. I'm not saying this is definately what it is but that is my first guess.
but i disagree, if they broke it, it IS their fault