My car is a 1995 Toyota Camey (I have 4 issues)?

When my car goes above 30 to 45 miles an hour my car shakes.What is the possible causes? Also My car the fan turns on right when i put the keys in the starter but the car is not started yet. Finally when I open the gas tank theirs a large amount of air that is compressed and the released; also it smells of gas when the car turns off?