At Ballina you can launch anywhere east of the boat ramp that looks good to you. You can also launch to the east of the bridge, just be aware of a few rocks off that little beach. Be especially aware of the tides as it can really get running in places. I didn't have much time today but had a quick sail just after high tide. Water was blue and clear all the way across the river. You can see my tracks below. Some very shallow water on the western end of my tracks. Also watch out for the rockwall on the south side, the big high tides like today has it sitting just under the water. At low tide it is exposed and makes some nice flat water. Wind can be pretty gusty and shifty in the river but somedays it is really good. Today was 15 to 30 knots and shifting from SW to S, to give you an idea.
I'm looking forward to trying Yamba. Is low tide best? Is mid tide pretty nasty with strong currents?