One tip is not to forget that the aim is to get everything out of your head, period. If the stress has gone you are there. You now have a system that works, at that point don't constantly change or fiddle with the system. Overtime you won't even think that you are doing GTD it is just the way it is and the way it has always been.
Don't stress over the system itself i.e. don't worry so much if you keep asking yourself "is this a next action? should this go in my calendar? is this a someday/maybe? should this go in my tickler? etc etc" once it is in, it is in and it is therefore out of your head, you can always move it someplace else when you do your weekly review.
good luck and keep at it.