1) You can't replace the main activities menu with the device menu but you can press the "Device" button to get a list of devices.
2) The website (your home page) has links to the online manual and many FAQs.
3) You can create a Generic Activity with all your devices and map any device commands to any Hard or Soft buttons. If you don't want activities to control the power of a device, then set the device power settings to "Leave On". The "Leave On" option is misleading. It should be named something like "Leave it alone", or "I don't want the activities to control the power of this device".