I have had three iPads--and have never gotten the Cellular type. It just wouldn't make sense for how I use it. Almost 100% of the time, I'm using it either at home or at work (and there's free wifeless Internet in both areas). That's what you should ask yourself, in my eyes. How often would you want Internet access when you wouldn't be near a free wireless?
Per your second question, I have always had the "normal" size iPad. My wife, however, has had both normal and mini. She rarely uses the mini--as her usage pattern is similar to mine (see above). The mini just isn't necessary for our needs. YMMV. The normal one can be fit in lots of mid-sized camera bags. The mini would make sense if you were out and about a lot--and would be without a bag that large. I really prefer the normal size for everyday use, perhaps largely because it's what I'm used to.
