What wind speed is needed for a 9 m and 12 m kites to water start a twin tip kiteboard?

Whoa, let me get on first; the answer to your question is dependant on the following:
1) type of kite (LEI or Foil)
2) Your weight
3) Type and size of board
4) Location (a warm northerly in QLD packs less punch than a cold Southerly in Vic or WA)

You would get away with a 4m foil wing mate

There should be a wind speed guide on your kite manufacturers website.

Cabrinha convert 9m. Cabrinha switchblade 12 m. Underground twin tip flx152x42. 74 kgs. Newcastle area

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kpracing said..
Cabrinha convert 9m. Cabrinha switchblade 12 m. Underground twin tip flx152x42. 74 kgs. Newcastle area

Switchblade has plenty low end grunt but is quite heavy so I reckon your "ideal" window would be 14 to 20 knots on the 12m and 17 to 25 knots on the 9m.