Yup.
Helium-4 (also written 4 He) is an isotope of helium. It is the most common isotope of helium in the universe. Out of all the helium on the Earth, 99.99986% is helium-4.
True. It is formed on earth mainly as a result of decay of radioactive elements. Alpha particles (a type of radioactivity) are just He-4 nuclei. I am not a geologist, but AFAIK there would be no reason that release of helium would be correlated with imminent volcanic activity.