Welcome to iMore!!
I can totally understand wanting to take good care of your investment. I too have an iMac and it's the main computer for my household... lol so I'm always making sure its clean.
Taken from
Apple Support Website:
When cleaning the outside of your iMac, first shut down your iMac and unplug the power cord along with other connected devices. Then use a damp, soft, lint-free cloth to clean the computer's exterior. Avoid getting moisture in any openings. Do not spray liquid directly on the computer. Don't use aerosol sprays, solvents, abrasives, or cleaners containing hydrogen peroxide that might damage the finish.To clean the display on your iMac, first shut down your iMac and unplug the power cord along with other connected devices. Next, dampen the cloth that came with your iMac—or another clean, soft, lint-free cloth—with water only, and then wipe the screen. Do not spray liquid directly on the screen.