Patterns are for suckers, so after some experimentation (aka ripping out the bottom twice) I settled on 2 strands and 9 mm needles for the bottom, single strand for the colourwork on 6 mm needles.
For the lace worker who is used to size 30 cotton and 2 mm needles? This is like speed crack. Each row actually adds length! Noticible length! I worked two patterns and it started to look like a bag. (I also started thinking that attempt two on the size of the bottom was probably a better choice, rather than hugely too big, but that's besides the point).
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Now I need to actually finish this and felt it and decide on what to do for a strap.