First, if you know that all your pics are going to be the same length, you can set a length for imported still images in “edit – preferences – import”. Your choices are length of comp or a defined length, i.e. 2 frames or whatever you want. Then you don’t have to adjust the length in the timeline (if each pic will be a different length, you’ll have to adjust it anyway).
Second, you can sequence the layer in the timeline in the order you want by ctrl-selecting all the pics in the project window IN THE ORDER YOU WANT THEM TO BE IN THE TIMELINE, drag them to the timeline, right-click on one of the selected layers while they’re all selected, go to keyframe assistant – sequence layers. Then the pics will be sequenced in the timeline in the order you selected the earlier.
Third, if you are animating all the pics the same way, you can either save an animation preset on one and apply it to the others, or use expressions to avoid creating a new set of keyframes for each layer. How you automate the animation kinda depends on how you want to animate. 🙂
Hope this helps,
Eric