See, I made it!
Knitted from acrylic but pretty nice yarn, with 5mm needles, exactly according to the instructions (and of course without gauge swatching - it ended up bigger than the original).
I also knitted the side in a lighter colour, and added some basic cabling.
The bag hasn't got any pockets, but it may get one or two; I'm hoping of using it as a knitting bag, as it's pretty 'stretchy' and will not be suitable for heavy objects.
Hooray for me for finishing my biggest object since!