1. Yes, it takes sometime to boot if you do power on cycle but this is common for android based STB and TVs as well. My Android TV also takes similar time if I do cold boot. Normally we switch off Airtel box using remote which is like sleep mode and takes hardly 2 seconds to get home screen.
2. Yes, that true to some extent. We can mark favourite channels but there no option to scroll only those favourite channels, like it can be done in HD box.
3. Live channels will be available for viewing using Xtreme STB as per your D2H pack. In mobile xtreme app, you can view all live channels if you have its subscription which is also available free for Airtel Gold or Platinum member. In Xtreme box, you need to have active D2H subscription to which Airtel Xtreme Movies and Shows along with third party apps. Earlier we can watch 3rd party apps even without subscription with some work around but Airtel has disabled it with recent update.
Hope it helps to decide.