Set Up for iOS
USB Midi Keyboard
Apple Lightning to USB3 Camera Adaptor with charging port
Not required for PC set ups or if using products like Korg plugKEY or wireless Midi adaptors with Bluetooth Midi LE.
bs-16i app from bismark (around $8 U.S.) or other SoundFont hosting app such as Soundfonts or Jamkoo
Optional audio interface for iOS/PC (not necessary but can improve sound and allow other functions)
This (or Bluetooth Midi LE device) needed if your keyboard only has 5 pin Din Midi and no USB Midi. (Also Apples move to have no separate audio out jack means iPhone7 users onwards will most likely need an audio interface).
[Eg. Steinberg UR22mkii. A smaller unit for 5 pin Midi is the Korg plugKEY for a compact setup and with this you don't need the CCK.]
Some keyboards may require a Powered USB Hub (approx $25) if the keyboard is drawing too much power.
In this case plug the Lightning to USB3 camera adaptor (previously called the Camera Connection Kit or CCK) into the Hubs main upstream port and the Keyboard into one of the downstream ports.
If you have the CCK that accepts power you can also use one of the spare ports to charge your iOS device while using it.
If you have an audio interface and it accepts USB power you can power your whole setup just with the powered hub if it has 4 ports and assuming your keyboard's USB connection also powers the keyboard (hubs with at least one USB 3 port are best as they provide a little more power). 1 connection to the keyboard, 1 connection to the interface, 1 powering the interface and 1 powering the iPad/iPhone via charge input of the CCK. The main out of the hub still goes to the data input of the CCK.