Engine: The Magnum 120 4 stroke won't have enough. I have an OS 1.60 on my Creek Staudacher, and it has just about the right power. However, the plane could use a heavier engine for better balance while putting the servos at the tail. I have to have the 2 elevator servos up front to balance out with the OS. The OS would fit into the cowl completely, which is nice. But I wouldn't recommend the OS 1.60 for 3D, because its midrange and throttle resopnse leaves something to be desired. Go with the Moki if you already have it.

Servos: "Hitec 525MG on the elevator halves and ailerons and a 645MG on the rudder" sound good. That's more than what you need, because the control surfaces are terribly huge. I'd recommend using stronger hinges for the rudder though.