I have an indesign file that's larger than needed. Is there a way for me to "scan" the document to find out exactly what files/objects are taking up most of the file space?
Here's the best and fastest way to know what resources are the biggest. You cannot "search" for a resource based on the link's size, but this is as close as I can get you to help you do what you want.
1 - Export your project as a package.
2 - Click on "Package"
3 - Click on "Package" again making sure these boxes are ticked:
4 - Open the "Links" folder where the files / links have been exported
5 - Sort out the files by size, the largest ones on top.
I'm aware that you wish to "search" for the largest file within InDesign. Such a feature doesn't exist to the best of my knowledge and research, so here's what I suggest if you have a large document with too many linked files that you want to clean up.
Other than that, you might be able to write an InDesign script, to achieve what you want, it's worth looking into it if you need to do this often.