I love your inspiration quilt! Size really depends where the quilt is going to be used. For a couch throw, I like ~60"x80". This is big enough to fully cover myself, but small enough to not be hard to handle. 100" square is a generous queen size - too big for on the couch, IMO.
Of the size options you listed, I would choose 81" square, but for myself I would likely make it one row narrower (70"x81"?).