None of my cars are complete ready to run ATM (crashed badly) waiting for new parts to arrive
Petrol can effect the wiring of the servos and etc , only apply petrol of metal parts , plastic will get soft and break easily. Use soap and water on plastic
Yes you can custom make one out of plywood , you can find printable blueprints with correct dimensions on the web. But some experience is needed to fit engine , servos , ailerons etc.