I tour with an iPad and wrote
an article about my experience.
It isn't realistic to use the iPad while biking. It is only for use before and after riding for the day. Mine, too, is the Wi-Fi only version, but I have take screen shots of map pages for reference later.
If I am touring in the US, I also take my iPhone, which can be made into a hot spot. I haven't powered my iPad by my iPhone yet, but see no reason why it wouldn't work, as long as I had cell phone reception. Any on-bike referencing to the internet I do with my iPhone.
Mostly, I use the iPad to handle email, surf the internet, write my day's summaries, plot the next day's route, and pass time in the evenings. It is much more convenience then trying to do the same tasks on a smart phone.