For the opacity you can use an expression that fades in and/or out. The expression still work if you trim or extend the layer. It fades in and out over the duration of 10 frames. You can just copy paste the expression to other layers then. Here's the expression:

fadeInTime = .5; // time (seconds)

fadeOutTime = .5;

Math.min(linear(time,inPoint,inPoint + fadeInTime,0,100),linear(time,outPoint - fadeOutTime,outPoint,100,0))

If you're not sure how to use it or nor really familiar with expression, here's a more detailed take on this expression:

https://bluefx.net/how-to-add-opacity-to-layers-footage-after-effects
http://bluefx.net