When making scalloped hems I find it is helpful to first measure the un-hemed skirt then divide the measurement by how many scallops you think you want. The number you get is how wide the top of the scallop should be. Play around with how deep you want it to be and if the scale and when you have it the way you want the final thing to be cut one piece of iron on interfacing for every scallop and iron it on to an uncut strip and pin it to the front of your fabric. Weird I know but there is a reason. Now you have a prefect template in the form of interfacing to sew along the edge of. When you have it sewn trim off the access and chip the top of every scallop so when you turn them inside out pressing them will be simple. Then press and trim.
When binding seams on a flared skirt make very sure what you are useing is either thin or you have a way to adjust the trim so it looks good. Always stitch the bottom edge first because it is the bigger of the two. When stitching the top I find the best time to add a dart to keep things from going wonky is when it become hard for it to sit parallel with the bottom.
As always if you have questions feel free to ask them