If you can afford a newer model then, by all means, get a newer one. Refurb Air 2's will probably be coming down in price with the 9.7-inch Pro hitting shelves on April 1.
On a side note, make sure whatever seller you buy from replaced the battery. Apple refurbs come with new OEM batteries and full warranties.
I know newer is better for longevity. But otherwise, no need to get the latest. I have the iPad Air first generation and it works great. My battery life is as good as it was new. I spend hours on it every day and have had no issues with it. So as said above, go with your budget.
For what you will be us be it for, the iPad Air will indeed be sufficient. Having said that, if the extra dollars is not a problem, go with the iPad Air 2. It's faster, has TouchID, a better camera, and will be supported longer than the original iPad Air.
i have an iPad Air 1st gen I just purchased a week or so ago. It's a 32 gb lte model for the price it was cheaper then some wifi only models. Personally when I initially upgraded to the iPad Air 2 I was disappointed the batter got smaller and my battery life suffered as a result. I felt no difference in use and couldn't care less about having Touch ID on a tablet. iPad Air is my favorite iPad to date. To be fair I haven't owned the iPad Air pro but the 1st gen air is a good buy still.