Unused languages, modules, blocks and themes can be deleted.
Usually the installation size of Moodle will be minimal compared to the potential size of course particularly if they contain images and multimedia or instructors do lots of course backups. It's courses where you will need to keep an eye on space usage.
I am testing Moodle to see if it would be suitable for what I need and my test server allows me only 100mb of space so that is why I am trying to keep it compact. If I decide to use Moodle in a live environment, I will find a larger region.
Thanks for your help,