I will meet you in the restaurant. --> Yes, this means you want the person to go inside the restaurant to meet up with you.
I will meet you at the restaurant. --> Yes.
The restaurant is at Zhongshan street.(maybe in or on?) --> Should be "on Zhongshan Street"
I am standing in a bus.(on a bus?) --> Usually we'd say "I am riding on a bus." You could say "I am standing in the bus."
I am sitting in a car (on a car, at a car?) --> Yes, this is right. NOT "on" or "at."
I am in a bar.(at a bar?) --> Yes, this means you are inside the bar; it is emphasizing location. You can also say "I am at a bar."