Honestly, the easiest thing to do for your first 2 or 3 dipes is to buy them precut from a place like diaperkits. That's enough to get you comfortable w the sewing process before investing in a lot of yardage/notions.
I like diaper flannel for the body, just realize that flannel doesn't absorb a whole lot. The body is there to hold the soaker and contain the poo. I like a soaker of cotton microterry (1st choice), cotton terry or hemp/cotton fleece. For a heavy soaker like my DS, he needs 6 layers, so i make a long narrow 3-layer soaker twice the length needed, fold it in half and stitch along the fold at the back of the dipe. This way you get the necessary absorbancy, but it also dries quickly and washes cleanly.
I also dont like sewing along the length of the elastic, i've found ot loses it's resiliency. I make casings and just secure each end.
HTH
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