I think you want to be sure to get the 64 gig model (there is no 32 gig for the ipad any more). My iPad 2 was a 16 gig, had no trouble saving 3 ebooks and monthly digital editions of a couple of magazines on it. So I saw no reason to get a bigger one when I bought the iPad Air 2 last fall. Turned out to be a bad decision. The version of iOS 8. on the iPad Air 2 (and maybe the iphone 6 too) uses so much storage space that I maxed out what it left available on the 16 gig ipad before I could finish loading the 2nd issue of Bon Appitit (I had 8 at the time, all on the iPad 2 with room for more)..I hadn't even gotten far enough to try loading the ebooks yet. A call to Apple support revealed that I needed to exchange the 16 gig for the 64 gig . Did that and all is well...at least when it comes to being able to store what I want to store on it.

I have no idea how much space nav software and charts need, but thought this worth mentioning.