We all walk this path, but we don’t all decide to take the same turns!
If you want to use the iPad, a powered camera adapter would be good if the iPad is running out of juice too soon. As for apps, any recommendations will vary depending on what exactly you’re wanting to do— record the MIDI data coming from the keyboard and then edit it, record just the audio coming from the keyboard and then edit it, or send MIDI data to the keyboard to do things like change sounds as you’re playing the keyboard or have the iPad play notes on the keyboard.
If you want to use the Windows computer, there are many programs for it as well, and you shouldn’t have to worry about the power running down (unless it’s a laptop and you don’t have it plugged into a power adapter).
By the way, if you’re wanting to “compose” your own music, there are also notation apps and programs that let you write music on either a single staff or set of multiple staves. Not only do they let you play back the written music to your keyboard as with a DAW or “sequencer,” but they let you export your work to MIDI files so you can load them in the keyboard (if the keyboard supports that and if it uses Standard MIDI Files or SMFs). If you’re just learning about music then you might not want to go the notation route— but then again, you might, if it helps you follow along with any lesson books that you’re learning from.