Not sure about Austrian but one carry on only is fairly standard outside the USA. Can you not fit your camera bag into your carry on (which, incidentally, should be within the permissible size - it's far more likely to be refused if it's too big than if you have two).
As to gate checking, yes you might be relieved of excess carry on at the gate, but it generally gets delivered to the carousel at your destination.
Finally, the number of carry on items is generally limited to one, but this is not rigorously enforced. Many people arrive with shopping bags from their airport shopping and are allowed on. Also, in winter, people have heavy coats. So you should probably be ok.