Sorry Michael, I also have little experience with Android equipment, I only use the nexus for this mount really, but out of the 16 GB storage I have, there is 12 GB or more spare so I don't think storage will ever be a problem.
It's best to check that the device as a few extras like GPS, Location, Compass etc. These apps can help and make life much easier, such as the "Compass" part of Sky Safari where you hold the tablet towards any part of the sky and it gives you detailed info of every star. Even with the Nexus I input my location manually in Syn-Scan ... only takes seconds to do and you only do it once.
The problem with the iPad...........from what I read ages ago it looks like running these two programs at the same time on the same device was a non starter so I veered away from those devices.
I went with the Nexus 7 ( the WiFi only ) as it didn't cost very much for experimentation ( £35 ), I thought the standard phone size is to small, and the 7" tablet was just about right for viewing Sky-Safari. And I would say all the problems I experienced have disappear using the Nexus 7. The Nexus in it's day was a very powerful tablet and it has a really good high resolution screen 1920 x 1200 so that is full HD on a 7" screen. I also bought a " Cooper Trooper 7-8” Tablet silicone Case" as it comes with a strap so you can hang it around your neck if you want and it also has a kick stand for use on a table