re: Sheet to Tiller or Windvane?
Tried sheet to tiller. Takes a lot of screwing around every time the wind shifts or changes its strength. Not a long term solution. Built my wind vane steering system for under $25.No problems in 28 years. Very expensive, commercially made ones don't work as well.
Buy a copy of John Letcher's book on self steering. There are much better alternatives to spending such a huge amount of money on one.
Post a photo of your boats stern.