Need information on .aep files and related stuffs

I have never used adobe before and in fact have no experience of Graphics design as such. .

I got an animation developed on freelancers.com. As a final delivery they are giving me a .aep file.

The size of the animation they sent me as .MP4 is 17 MB, while the size of .aep file is only 2.7 MB.

I want to make sure that I have got all raw files, so that in future I can modify them as and when required. Now I have two questions :

1- The .aep file of 2.7 MB is sufficient to recreate the 17MB .MP4 animation?

2- What tools I have to install in my PC?