To answer questions, the wrong side looks not that great to be honest. It's all revere stockinette which is fine, but the square where the butterfly stitch exists sort of looks like an indented square. It doesn't look terrible, but I'd definitely do a swatch to see what you think.
Adjusting for size...The adding 10 stitches per size refers to the body of the skirt so we'll have to do some math to figure out the cast on stitches.
For size 4, it was CO 226, body of skirt was 150, so that cast on is 1.5 of the body. So if you wanted to do a size 6 at 160 stithces for the body, I'd cast on 240 stitches. If you want a larger frill, cast on more stitches (I have to say dropping the stitches off the needle to provide that lacy effect was so thrilling for some reason!) Please double check this yourself though!
And like I said it looks small on the needles but it did stretch out some (although I suppose it could be altered if you used a different type of yarn), I did do some serious blocking.
Happy Knitting :lol: