How much space does an emulator take up and will i get any viruses from it?

I just got a new computer from Toshiba and i was thinking about putting an emulator on it but i also need the computer for college notes and school work so I don't want to take up too much space on it and it definitely can't give me a virus for said reasons. If I do get an emulator, I'm also torn between it being a gamecube, xbox, or playstation 2 emulator. If anyone could help me answer my questions, I would greatly appreciate it. Thanks.