iPad Mini 4 WiFi + Cellular. I use FreedomPop for the cell. It's free for 200MB data each month after I spent $10 on the sim. It's convenient to have data and GPS in the iPad. I've also dedicate the iPad for drone work so it is not cluttered with software and I only update the software when I have time to test it for compatibility. I also make sure the DJI app is the only app running.
iPad mini 3 but I turn of caching video and it’s never failed. It also has a speaker problem so I don’t get any annoying feedback which is ok as long as I spot error messages on screen. Sound works fine on headphones or Bluetooth
I use this one from Amazon. It’s a folding hardboard, covered in PU plastic. Fits easily in my case and installs quick. There are several manufacturers of this type. Or you can fashion one yourself if you’re handy.