You don't necessarily need to put Windows on the Mac to get and use Office. If you get a subscription to Office 365, Personal, or Home, you can have Office for between 1 to 5 computers.
If you're anything like me, a mostly basic user of Office, the Mac version will work just fine. I've read other users, who use some of the more advanced features (don't ask me what) say that sometimes there are differences between the Mac and Windows versions of the suite.
Plus, you can't get Access or Publisher on the Mac. If you need those, then you'll need Windows.
For putting Windows on the Mac, you have two options: Boot Camp and virtualization. I prefer virtualization and use VMware to host Windows on my Mac. Then you can install Office for Windows on it and be ready to go, plus you can use OS X at the same time.
Boot Camp means you install Windows on a partition and have to restart the computer to get to either Windows or OS X. Typically, many people who do the Boot Camp installation, do so, so that they can play games or do other hardware intensive tasks in Windows where they need native access to the hardware for performance reasons.