I think compressing would slightly slow the access time to the files. I wouldn't do it unless space was at a premium. I'd buy a larger drive rather than compress if space was running out.
Indexing is useful to search the contents of files using the Windows search function. Normally, I would think you would want to search the contents of your ORIGINAL files, not the backups---if you are the type to search file contents and use the Windows search function at all. So you might index the drive that contained originals, but not the drive that contained backups.
Personally: I do not index or compress any of my drives. I do not use Windows search. I never search for file contents. I use a third party tool to search file titles only.