It's possible to gain resonance, e.g. to have both static and dynamic, at different amounts (or even all three). But resonance is neither a good nor a bad thing. They can help you with certain effects, but they will make some effects easier to target you or they will make certain effects more difficult to make them happen.
Resonance is not something that you can select in an optimization sense - it's more of a fluff thing. It's a way to describe your personality.
You usually gain resonance if you make something really really bad (such as botch a powerful magical effect), prolonged exposure to powerful effects/artifacts/etc and if you "cast" effects that fit thematically in a specific resonance (e.g. if I'm casting scanning effects constantly for three years, without casting anything else, I might get some static resonance).
The maximum arete you can have is 3. I'm sorry, but 3->4 is a huge power up, as spheres grow exponentially. You can't have Life 4.
