License / copyright

[donquixote]

I added a LICENSE file copied from somewhere, and I'm saying GPL in composer.json.

But coming from Drupal land, where the Drupal packaging script does this job for me, I am probably doing it wrong. I like OpenSource, but I never spent much time learning about licenses.

• Is it preferable to use GPL or MIT, and why?
• Is it even possible to change the license after release?
• Is the license per file? Per git commit? What if someone finds a git commit that is not properly licensed?
• Where should I give attribution to people I copied from? In every file (e.g. the fixtures), or is it enough to have one document talking about authors?

Ouch ouch ouch..
I want to play nice with everyone, but I need some babysitting.