Your 'video' doesn't exist in MEP until you export it as a video file (xyz.mp4, abc.wmv, etc). What you have in MEP is a project (a relatively small MVP file) specifying all the components of your potential video.

Once you have exported the project as a video you can then, of course, see its size in the familiar ways, such as examining it in Explorer under the Size column, or opening its Properties, or using a tool such as MediaInfo, which provides much more useful information.

https://mediaarea.net/en/MediaInfo