Re: Neck shims
A shim should be used if the tremolo is too low (or high). There is no benefit to putting one in if there isn't a need for it.
If you do a full shim, you won't have any gap. People here have said it's overkill, but I always cut my own shims. I buy sheets of maple veneer, and draw a basic shape on it using the neck heal. I cut outside that line and see if it fits in the pocket. Keep sanding down the edges until it fits absolutely perfectly. Then I take it out, and make a pencil mark across a little over one half of the area. I then sand off the pencil mark, putting much more weight toward the end. When done, I put it in the pocket and attach the neck to see if I sanded enough. If not, repeat the sanding process. It's really that simple.