I always use Quaternion. I never even consider Euler. The times I've used Euler I end up with a jittery animation. It's just not a polished feature. The easiest method (without Euler curves) is to use "Tripling". Where you duplicate the animation keys twice, and export the middle segment. For example, if your animation is…
Oh, and as far as looping and offsets, I've discovered a trick. Loop everything smoothly, then take the limb you want to drag behind, for example. You set a key X number of frames before the end of the animation. Make sure tangents or tcb is set, then delete the last key frame, slide all keys over so the new end key is on…