I had the same questions. In short: You're right. The longer throw (1.2 cm) is for the pitch trim, by far the most important trim tab controller. Make sure it's robust. I followed the plans. Important both to allow hand flying and to reduce autopilot servo loads.
If you install roll trim, you can use a 1.0 cm throw Ray-Allen servo for that. It's detailed in the plans, downloadable chapter OP-38 as using T2-10A, but is optional. I think adjustments can also be automated by autopilot to relieve autopilot servo loads. There's a Vans kit that has all the pieces.
There are multiple inventors out there who have made in-flight-adjustable yaw trim systems. Some are springs on control rods (similar to the wing roll pitch), some are small trim tabs added to the rudder, and either could be controlled by yet another servo or could be ground-adjustable. I don't know what servo is best to use for this, but I'd guess a similar one to the roll servo would serve. I'd lean toward ground adjustable first.
I'm planning not to install adjustable yaw trim, but instead to use a yaw damper autopilot servo, likely supplemented with a fixed small rudder trim wedge sized for typical cruise speeds, chosen by taping on wedges during phase 1 trials. The designs I've seen to look elegant though and if climb-out yaw correction is hefty, I could change my mind. Everyone wants the chance to rebuild their slightly imperfect rudder, right?
