Lets say I have a shaped collage of photos like in below video.
What I want to achieve is a small video where initially it is empty and photos fly in and fill the places in the heart shape or whatever other shape I make.
I would suggest working in reverse. Start out by arranging all the images the way you want them to appear at the end and set position keyframes on all of them at the end of the sequence. Then move to the beginning of the sequence and set keyframes on the positions and start dragging them all out of frame. You can then drag the starting keyframes around to adjust when they start flying in and adjust the end keyframes to alter when they arrive in the collage. Just keep moving the positions and the timing until you have something you like.