1. Not sure - if you've got a photo that may help.
2. Yes - pre drill - usually aim for 2/3 of the diameter of the screw - alternatively the diameter of the core of the screw - not including the thread.
3. Check out http://www.buildyourownguitar.com.au...ead.php?t=1826 - different guitar - same problem and solution.
4. Minimal gap - probably a photo would help to understand what and where.

Hope that helps.
B