Hi Mark,
I grew up windsurfing in Ballina (about 10 years ago now).
I would sail at the Richmond River Sailing club (yellow cross) in SE-S & W winds. Fairly easy to sail although the tide runs quite quickly so need to keep that in mind if the wind is running with the tide.
In nearly all other conditions I could sail in north creek (orange cross) launching at the serpentine although low tide can expose sand banks and become shallow in a lot of spots.
As tomp mentioned, the other side of the bridge can be a bit tricky as the tide can be strong and it can prove hard to sail back to shore where the wind is sheltered in a NE.