Yes, Honor 8 has 3.5 mm music jack.
Yes, Honor 8 does have IR sensor. You can use it as IR remote control with most of appliances, which support basic IR reception.
No. You cannot record 4k videos but you can play 4k videos on Honor 8.
Honor 8 has the wide aperture of f/2.2 for the rear camera and f/2.4 for the front camera.