You need to go on top of the Corcovado! (I´m sure you will)
Well when we stayed in Rio the train wasn´t in service for some reason and we get up to the top in one of those tiny busses (7 to 9 persons)
What a hell of a ride that was!
And make sure to go on top of Sugar Loaf Mountain too. Not so high as the Corcovado but a whole different view on the city.
For food: Zona Sul is ok! Normal price supermarked like Rewe in germany. You can buy german beer too, but for very high prices, and it´s not worth it.
Brazilian Beer is very good! You get everything you need there. You will find many things that you can buy in germany too. It´s not so different.
Don´t forget to eat Feijoada on wednesdays or saturdays. Traditional style stew with pork,beef, rice, beans and farofa.
And try fruits! Every fruit you see! Never thought that even bananas taste so much better than here.