I have a few questions, to help make my character and backstory, please.

What is/are the source of powers?
How common are people with powers?
Are powers determined by any particular cause or reason, such as cause of trauma, genetics, or personality? Or perhaps linked to a particular relic/technology or god/alien?
Can people with powers get mutations, either temporary or permanent?
Does gaining powers have any effect on a person's psyche? 
You say we are in contact with aliens. Does that mean just the governments, or do they walk among us? Could our characters be aliens? 

I know you want to leave a lot of the world building up to us, but please let me know if you already had any answers in mind to these questions. Thank you. =)