Yes, considering the display size and battery capacity, Honor 8 is quite light weight. It weighs just about 153 grams.
Yes, Honor 8 supports VoLTE. You need to update the software, though.
Yes, Honor 8 does have IR sensor. You can use it as IR remote control with most of appliances, which support basic IR reception.
Yes, you can play 4k videos on Honor 8.