The Pleiades Hat is one of 16 glorious designs in Stranded Knits, a superb technique manual and pattern collection that Ann created for Rowan Yarns.
The PDF pattern includes clearly illustrated tutorials for the twisted German cast-on, and for the centred double decrease used in the hat crown.
Tension/gauge for the hat varies according to size as follows, with the gauge for the smallest size given first. Choose the needle size with which you get the given tension for your chosen size. The number of stitches cast on and number of pattern repeats also varies according to size.
28(29:31) stitches and 30(31:33) rounds per 10cm/4" in stranded pattern after blocking.
Please note that Felted Tweed DK is akin to a US sportweight/heavy fingering.