I am not omniscient in Warcraft lore, but I thought I’d outline my two coppers, and you can take from it what you will (I’m sure someone more knowledgeable in the lore will reply).
Do keep in mind that Eastvale, Elwynn, Redridge, Brightwood (now Duskwood), and Westfall were completely overrun by the orcish horde in the first and second war.
Thus your character and his loved ones necessarily fled from Eastvale during that time (which gets confusing, because Blizzard decided most WoW expansions lasted only one year), around 33-26 years ago… So if your hunter is mid40’s, he probably spent his 7th-14th year as a refugee; from what I’ve read, most likely in Lordaeron.
As for the hunter specific lore, my knowledge is pretty thin, so here’s how I see it:
The bond my hunter has with his pets is much like the bond between animal lovers and their pets. (If you are, or know, such a person yourself, you know that bond can be just as strong as family ties:)
Nothing magical, though, in my case, just a strong mutual trust and affection.
I picture my hunter communicating with his pet(s) with subtle words, sounds, and gestures - and the pet(s) communicating with him in much the same way, except words, of course.
No communication would be necessary to ask for help if being attacked (assuming one could see the other); Naturally, either of them would take great pains to protect the other.
Personality-wise, my hunters’ do not change according to their current pet, but I do see some logic in it. I’d have no problem with that 
(I even think examples can be found on Earth…)
In my cases, the animal companion does not affect the senses of the hunter, but if the animal sensed something, it would let the hunter know.
Also, my hunters have spent most of their lives out in the wilds, so their senses are more developed than those of city-dwellers.
Pain is not actually shared between my hunters and their pets, but strong compassion is a significant part of the bond they share, so I’d say they almost share pain, but not literally.
(That being said, I’d have no problem with hunters sharing pain with their animal companions. If some humans can shapeshift into ferocious, powerful beasts, amazing aquatic animals, and even birds… surely a hunter and his animal companion can feel each other’s pain.)
My hunters would be utterly devastated if their animal companion died, not because of magic, but because they love their animal companion just as much as a family member or a life partner.
That’s my take on it, but like you, I would really like to see some lore about it.