Borders will be 3 1/2" - 9 1/2" dividable by 3's again. (The center block, all borders, cornerstones, or whatever should be carefully squared each step of the project.)
Option - in lieu of any one of the first 2 rounds, the block may be turned on point, if appropriate. Triangles are then added to each side of the "diamond" to make it into a square again. Appliqué or embellish the corners. You do not have to start with small. Make it so that it looks good to you.