Not really sure what you mean by the base, the ventricles contract from the Apex (which is at the bottom) upwards.
Purkinje Fibers actually makes the ventricles contract.
The ventricles contract.
When relaxed, the atria expand, and then the ventricles contract.
The pulmonary artery and the aorta lead upward and away from the ventricles. Since the ventricles contract from the bottom, blood is more efficiently pushed out of the heart.
Yes, atria contracts before the ventricles.
Systole
Into the heart
contract
The right ventricle pumps blood to the lungs.
The ventricles contract to pump blood out of the heart.
They normally contract together.