The current version 6.1 of SongBook+ runs on all iPads with at least iOS 13.
That is iPad Air 2 and newer, iPad 5 and newer, iPad Mini 4 and newer and all iPad Pro (both sizes).
(Or the other way around: iPad 1, 2, 3, 4 and iPad Mini 1,2,3 and iPad Air 1 are too old for iOS 13.0 and therefore too old for the current version of SongBook+)
The storage size (32GB, 64GB, 128GB, 256GB,...) is not that important as long as you don't want to store countless photos, music and even videos on it or install many games. The PDF files needed for the SongBook don't require that much space.
On older iPads, an older version that is still compatible with the respective device can be installed if SongBook+ (no matter which version) has already been successfully installed on a device once with your Apple ID. Otherwise it is a bit more complicated, but also possible. You can find a description here: How can I install SongBook+ on an older iPad?
Here you can find a page on Wikipedia with all iPad models built so far and a listing of the technical specifications: https://en.wikipedia.org/wiki/IPad
SongBook+ version | Minimal iOS/iPadOS version | Supported devices |
6.1 | iOS 13 |
|
6.0 | iOS 12 |
|
5.0 | iOS 10 |
|
4.0 | iOS 9 |
|
Here you can find a page on Wikipedia with information which iPad and iPhone models support which iOS versions: iOS version history