Seamless skirt design

I am planning to design myself a seamless skirt using a cable pattern for the body of the skirt and ribbing for the waistband.

I could go either top down in which case I would increase or bottom up in which case I would decrease.

Either way I found out how to calculate how many stitches between increases or decreases and how many rows between increases or decreases. Since I am using a cable pattern for the body, a decrease like p2tog or an increase like pfb would be good to use(or possibly a M1A which is basically like a 1 stitch cast on)

For stitches to increase per row, it is basically up to me. For rounds between increases I would divide the round gauge by the number of increases per increase round and a similar thing would apply to decreases

Since there are going to be probably close to 200 stitches(definitely more than 100 stitches, that’s for sure) in the ribbing(I will use a US 8 circular needle for this entire skirt because it is the longest non-interchangeable circular I have which means less bunching up while knitting) and I have noticed very little difference between round gauge and stitch gauge in the round and row gauge and stitch gauge flat should I just knit for example 20 stitches of ribbing and 20 rows of ribbing with no border and knit the same stitches and rows in stockinette with a garter stitch border to prevent curling to decide which ribbing I want to use for the waistband and exactly how many stitches I will need for the waistband or should I go a step further and knit a proposed waistband in said ribbing, try it on to see how comfortable it fits and how elastic it is and decide what ribbing to use from there?

very useful