Arriving at the Alpine Route and tickets

After a night at Matsumoto we want to visit (7th November) the Alpine Route, but we want to be sure that weather is good just before we go. As we have JRpass we can go straight from Matsumoto to Shinano Omachi and save the time required going first to Nagano. But can we buy the Tateyama Kurobe Option tickets at Matsumoto ? If not – Is there a possibility that we go first to Nagano and there will not be any more tickets? Is it better to go from Shinano Omachi to the next station (Ogizawa) and buy tickets there? What is the letest hour entering to the route ? Any recommendations ? Thank you !