About PvP
 

How do I set my server up to be a PvP system with -/+ 10 level difference?

Make it PVP by changing the ServerType variable in the variables table to 1 (That's off the top of my head, I think that's right). Easy shmeazy.

As for restricting PVP to that level range... There may be another way, but the only one I can think of at the moment is to edit the code and recompile. You're probably looking for a function in zone/aggro.cpp called something like 'IsTargetAttackable.' It returns a boolean value, true if the target can be attacked and false if not. You would just need to add something like:

If the absolute value of myLevel - yourLevel is greater than 10, return false.