hey phil, to start with: light winds are much harder to ride waves in. you need to have good kite skills just to keep the thing in the air when it's less than 15 knots & 3ft plus.
go and have some lessons- a decent instructor will set you on the right track and give honest advice about what gear to buy.
and btw- you think you will only kite when it's too light for windsuffering, but before you know it the pole will have sat unused in the shed for a couple of seasons and you have a full quiver of kites

. better to realise it now and sell your windsurfing rigs while they're still worth something...