I've never used a jig for the perhaps hundert strings I've made. I just pull off strand and hold it up against the braced bow, overlap what looks like enough on each end. Longer is better than shorter, then you can trim once the string is done if necessary. Made dozens before I ever bought a serving jig. 40# or 50# "Spiderwire" or other braided fishing line (Dyneema) works perty good for serving material if you can find it cheap (Walmart closeouts at the end of fishing season). Just volunteering.
On a two color, two ply you first measure and cut one color, staggering the ends if you don't use a jig. Then just build another ply (same number of strands 1/2 the total count obviously) the same way. Then you twist these two different colored plys together. Same with a 3 ply for that matter, just 1/3 total strand count for each ply.
Padding loops is when you cut some strands perhaps 8" to 10" long, again staggering the ends. I do this by starting with equal lenght strands, then just offset some of them. Then you wax these into your primary bundles, where the loops will be, before you start twisting each loop.
For "skinny" strings I find padding the center to be a pain, so I just either double wrap serving, use enough primary strands in the main string, or a fat enough serving material to fit my nocks. There's a recipe for each string material, serving material and nock size. I find 15 strand FF, single wrap Nylon fits the Bohning 5/16" index nocks I prefer.