Plug gap should be 0.020 - 0.024", or 0.5 - 0.6mm.
With bike on stand and in neutral, there should be 1" to 1 3/8" slack in the chain halfway between the sprockets. Measured by pulling the top half of the chain up away from the swingarm from its resting position.
The stock pipe is actually very good, especially if you want low end and smooth power delivery. IMO, if your suspension is stock, you'll be better off spending your money on that (Factory Connection is excellent) instead of the pipe.