I always buy the highest GB size available , as it tends to take about 3 years to be the lowest.Funny you say that. I'm still rocking my 2011 iPad 2 that's very slow running iOS 7. Been reluctant to upgrade since it's only a web surfing/Youtube tablet for my kids.
(Apple takes it's sweet time to increase GBs as we know)
If you have a 2nd Gen 64GB iOS 9.3 is fine.
Also, just surf with it, soccer highlights, magazines, newspapers, youtube and some games. Does all of it well.