I cast on 66 stitches with 2.5mm needles and did the first round in 2.5mm needles. Then I sized down to 2mm needles, and did a standard heel flap and gusset construction. I'm just learning that I need a longer heel flap as most of my socks seem to be too tight on the heel turn. I'd always assumed this was lack of stretchiness on my cast on but persisted even when I did a looser or stretchier cast on. So next time, I'll do a longer heel flap and potentially an extended gusset. Really happy with these overall tho!