For the dissenters of "fill"---this design looks like it would be "enough" quilting, BUT, if you don't follow up with
background "fill", the parts that have no quilting will puff up and make it difficult to see the lovely feathers.
Something to consider. If you add a tiny hand stipple after all the feathers are quilted, you will not have to premark.
If you go with a 1/2" grid you will need to mark it before any quilting is done or you'll have a hard time keeping the lines
from appearing to wobble as they go across the quilt. In fact, I always mark background grids before layering.