#1. Left Hand Thread as mentioned above by WNG is your key
#2. ----
#3. You can do it that way a lot easier than lacing a rim not using all the rim's holes (I've tried with a 24 hole rim and 20 hole hub - I was building a square wheel as I raised tension). The harder part is calculating spoke lengths. IIRC on the 20/24 mix I had 4 different spoke lengths.
__________________
72 Frejus (for sale), Holdsworth Record (for sale), special CNC & Gitane Interclub / 74 Italvega NR (for sale) / c80 French / 82 Raleigh Intl MkII f&f (for sale)/ 83 Trek 620 (for sale)/ 84 Bruce Gordon Chinook (for sale)/ 85 Ron Cooper / 87 Centurion IM MV (for sale) / 03 Casati Dardo / 08 BF IRO / 09 Dogma FPX / 09 Giant TCX0 / 10 Vassago Fisticuff