Its summer here, now!
Don't worry about the lack of reaction to NAC, it isn't compulsory! The thing is, if you aren't very badly affected in the first place it could be a long while before you notice if anything is working for you. It might even be several years down the line before you realise that you have had no further relapses.
If the Australian MS Society is anything like the British one, they will push CRABs very strongly to the newly diagnosed. Not with me, though, because I wasn't diagnosed until I had become SPMS, and so beyond help. But carry on thinking out loud: even if you do opt for avonex, you can take antibiotics as well. Quite a few people do, at least to start off with.