I would like to distribute a Python script (with JavaScript/CSS and third libraries as jQuery, Bootstrap) under a free license, but I have some questions:

1) Should I indicate the license in all files or a single text file with the license in the root of the software enough?

2) Should I indicate the date in the license and why?

3) Can I put the text of the license under another license (e.g. Attribution-ShareAlike 3.0)?

Thank you.