FeedingIt uses very minimal space on the rootfs. There are only a couple of text files that are needed for the shortcuts/dbus, a launcher script and a couple of icons. It's quite under 100kB if I remember correctly.

If you use the image cache, that is stored in /home/user/.feedingit/ and can grow fairly large if you have feeds using large images, but that's not stored on the rootfs, that's the 2GB disk.

As mentioned, if Opera is supported by the browser-switchboard program, opening links to external browser from FeedingIt would open in Opera.