You really do need to zigzag a fabric like this, especially if it’s rayon, as this one is. The gathered edges still curl, but they’ll be zigzagged all the way down, making raveling seams less ravely. If you’ve got a serger, that’s an even stronger/better edge finish.
Length is a personal thing. Personally, I think mid-calf is good, but I know I have to be careful. Just below the knee is too short for me, mid-calf just focuses attention on my fat calfs, so below the fullest part is my choice. Then I don’t have to lift the skirt every time I climb stairs, and summer breezes can keep me cooler. (Thanks to Karen for taking some photos!)
What’s your choice?