If nothing else, you need to tell us what version of Windows and what you want to do with it (e.g. https://forums.macrumors.com/threads/1177448/) to get a useful answer on size. There are many kinds of school work. What do you mean by that.
If you aren't going to go on any shady websites and download anything you should be ok, but just to be safe I would download Avast! Antivirus software. It's free and works quite well