I love the attic window pattern - this one is very pretty.
About the quilting. Here are some options:
Quilt SID down the main lines (where it is continuous) both directions. Then you can start at the outer edge of the white panel and SID til you get TO the miter, and angle the SID down the miter. At this point, you can either tie off and start a new line at the next white pane, or just follow the already stitched line til you get to the next white pane.
The flower centers, you can either tie the squares with floss, or you can do some outline quilting on the flowers, or you can add one large(ish) flower petal in each square.