how to add 3d objects to a footage

I want to add 4 cube dies to a footage. I created the cube, tracked the footage, created 4 nulls from the track points on the flat surface and pasted the positions to the positions of each cube.

Then I animated them by rotating the z rotation and moving the x,y,z position in 40frames.

For some reason, it feels like its not realistic enough and I really don't know what else to add or do. I tried a couple of ways to add shadows for each cube and I wasn't successful (I spent a looooot of time experimenting here and there). The shadows were not casting on the surface in the footage.

I have attached the file here. Any further advice on how to go about this?