Tyre width

Hello, and indeed I bought white rims, 17 inches and 8J wide, but just without tires. Would fit tires from 215 to 235. Since the coupe with front drive does not like wide tires at the front I thought of 215 front and 235 rear. Once appearance and once driving behavior. But some advised me not to do so and meant if I have 2 235 back on it 1. the fuel consumption by 1-2l, 2. the handling worsens (which after the installation of the subwoofer with a kitchen plate very unfortunately had to) and 3. it is not good for the car. However, since I can’t understand 2. and 3. and 1. I seem a little exaggerated I am not sure what to do now.