Every break is a little different, but you are right - it makes sense to time the sets and catch the backs of the waves as long as you can. Usually the first 2-4 will be the larger clean out sets, with a lull after, so I try to actually ride the last one in.
You probably are used to turning on the wave and digging in your paddle with the monohulls, but on the tri you can't do this. You'll want to stay as square to the wave as you can and make any rudder changes as smoothly
as possible. It gets VERY sensitive at high speed, and on an angle. Use the fins sparingly and keep them tucked until needed.
It's much easier to catch waves that travel WITH the wind so the sail can help. Unless I am "thrill" surfing, I keep the sail reefed about halfway and a slight dagger in the water. Having a lot of sail is great until it overpowers the rudder and begins to steer the boat. For that reason, you may need to adjust both the sheet and rudder as you surf.
For instance, as soon as one wave passes, you may want to sail sideways to the next one, on a fast beam or broad reach (to build up speed) and then turn smoothly towards shore, easing your sail and pedaling until you catch the next face...avoid twitching your rudder side to side.
As you depower, trim your sail again and use the fins to help you going in the right direction (straight toward the beach!!).
I would love to hear advice from other experienced wave riders... or watch more youtube beach crash videos.