Q: I have and evap leak. I don't know where.

If your vehicle has an EVAP system leak, the Check Engine Light will normally illuminate, because a Diagnostic Trouble Code has been stored, and the Mechanic can use the Code that was stored to start his or her Diagnosis.

The odor of gas could be from the EVAP system but there are many, many other possible sources of liquid fuel leaks (as opposed to vapor leaks in the EVAP system) in the fuel tank, fuel lines, fuel injectors and so forth that can account for fuel odors. If you do have an EVAP system leak, typically a low pressure smoke machine will have to be connected to the system in order to find the leak source.

Driving a vehicle with "most" EVAP system faults will not damage the vehicle but driving with LIQUID fuel leaks could be potentially catastrophic especially if the leak is under hood, near something hot, and if the leak one day becomes "large". So, the concern is not so much the vehicle but the potential for a fire or explosion that could hurt you.

With regard to the coolant cap, that is easy to resolve. The steering wheel locking up is a concern and should be addressed. I would say after the gas leak is addressed and the steering locking issue is resolved, after that the vibration issue can be diagnosed.

To avoid any unnecessary repairs, my advice is start with a fuel leak diagnostic by a certified technician, such as one from YourMechanic, and then deal with the other issues in turn.