You can loop a single property, like rotation with a loop expression. Alt Click the rotation stopwatch, then paste in the following expression:
loopOut( “cycle”, 0)
There are several loop expressions, details and examples of all in the comp “Intro”, here:
https://www.creativecow.net/show.php?page=/articles/ebberts_dan/layer_looping/index.html
If you’re talking multiple effects and transformations, then it’s often easier to just render out one cycle of the animation uncompressed go to the last keyframe, (“N” sets the Work Area End, then Render), then re-import and select the footage in the project window, right click , Interpret Footage>Main> And in the Interpret Footage Dialogue Box put in the number of times you want it too loop (bottom of box).
It sounds like you might want to know about presets too, select all effects, masks and properties changed, then Animation>Save Animation Preset. Then when you apply preset, your animation is recreated on that layer. If you’ve added loop expressions, then you’d have a looping preset to apply to any new layer.