For what you want to do, and what you have, a Mac Mini is a good choice, and probably all the computer you need. If you do get a notebook and/or an iPad in future, they will integrate to make a convenient system.
It is OS X that makes a Mac. It seems pointless to get a Mac to mainly run Windows.
A Mac comes loaded with all the productivity apps you need to get going, but you can load the likes of Office for Mac, and Lighthouse and other apps, which run on OS X, if you don't like the Apple's Pages, Numbers or iPhoto.
I have owned 2 Mac Minis, the original 2005, and am now using the 2009 model. I don't have Windows installed. I do have Office for Mac installed, but seldom use these days. Pages and Numbers may lack all the features of Word and Excel, but I find them easier to use. They open Office files ok, and can export work as Office documents too.