Hi Kelley! Welcome to the board!
When batting recommends quilting every 4 inches, that it the maximum spacing you should allow between your quilting lines. Any less will allow the batting to shift too much, and could lead to deterioration over time.
I would probably do diagonal lines like Prism's link. If you go up the diagonal of every block, your quilting lines will be about 3-3.5" apart, which meets your batting requirements. I also find the diagonals visually interesting, and easier than staying neatly in the ditch.
Please post a picture when you're done, or even just of the top - I think everyone here likes pictures!