A:AnswerHello, The K480 does go into a sleep/low power mode when not in use, but it's highly suggested to turn it off especially when transporting it. Here's a link to the product support page and some FAQs: https://support.logi.com/hc/en-us/articles/360025179374--FAQ-Bluetooth-Multi-Device-Keyboard-K480.
A:AnswerYes, my son switches between his iPhone and iPad constantly. Works with messenger, regular text messages (SMS and iMessage), wechat, whatsapp, etc.
A:AnswerDon't have a kindle fire 10, but this is a bluetooth keyboard and should pair to any device that supports bluetooth keyboards. I pulled the specs for the kindle fire 10 online and it should pair and work well with this keyboard.