No. You cannot record 4k videos but you can play 4k videos on Honor 8.
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.
Honor 8 has the wide aperture of f/2.2 for the rear camera and f/2.4 for the front camera.