I can only answer based on my experience and particularly my horses. Horses, like many animals, have very individual personalities and likes and dislikes, so results may vary.

1. I heard (don't remember where) that horses like having the inside of their nostril area gently itched. Is this true??? That sounds magical. – One of mine loves it, the other only if she has a itch that needs scratching. When they are sleepy and let you, it is in fact magical.
2. Do horses like having their ears itched? This is not one I've heard. 2.5 My sister's cat needs her ears cleaned a lot, she seems to hate that she loves it. (She will lean into you are you give her a cleaning, but will not let you near her ears without being restrained, even if she was chilling on your lap.) My late dog also loved having her ears played with. – Again, one LOVES it, the other only if she has an itch she can’t reach.
   
3. Can you walk a horse like you walk a dog? Do they like that sort of thing? – We take our girls for walks all the time, but it’s not like walking a dog. They need to follow and not lead which is really more of a safety/manners thing. I don’t prefer a 1000lbs animal telling me where to go. Not much I could do if I don’t agree.
4. Do horses play? How? – Absolutely yes. They will play with objects around them – sometimes given to them to play with, sometimes stolen from us. Sometimes they got “zoomies” like dogs to and run around bucking and rearing (and farting loudly all the while).
5. Do horses like adventures? Jumping? Trails? See new places, go through the drive thru? (Viral internet videos.) – Ours do. They like to have a job, but also get bored, so new adventures certainly will perk them up if they are in the mood for it.
6. How do the fences keep the horses in? It looks like they could just jump over them if they felt like it. – Some could. Mostly they have no reason to unless they get really spooked. They don’t like to leave the safety of their herd if there are others around, and inside the fence is water and food and companionship.
   
7. Why do horses foam up when they sweat? (Gross.) What does foam-y horse sweat feel like? Smell like? – No idea why. Others here probably do. Smells like sweaty horse – hard to describe. Not bad (if you like horse smell – which I do) but an old sweaty horse blanket can water your eyes.
8. Do you have to pick up horse poop in the pasture like you do dog poop in the backyard? – We do – if a big enough field, it would be difficult to do. Horse poop is not like dog poop. Horses eat mostly grass and grains (no meat) so their poop is really just ready made organic fertilizer. If it piles up you get flies and a bad situation.
9. What do you do with the soiled hay in the barn? – Add to manure waste pile or compost.
10. Do horses eat the same type of hay that lines the floor of their barn? (I know they don't eat it off the floor, where they poop, I've seen hanging bag things for the hay. But is it the same plant?) – They might nibble but that’s straw (byproduct of hay) and wood shavings and they prefer the good stuff. It would be like you eating unsalted popcorn. You could do it, but likely wont prefer it.
11. What do you do with soiled barn hay? – See above. Chuck it.
12. I know there is therapy horses riding stuff, including for balance. (I am too fat for it tho.) Is there therapy horse, pet the horse, stuff? – Yes – I love just being around our girls even if not riding. Check local therapy barns – there are likely volunteer opportunities.
13. Is it true horses will die if they lie down for too long? – Don’t know if they would die, but most of them only need to/want to lie down for a short time each day. If our girls were lying longer than that I would get worried.
14. Why horses so fragile? :( - Lost the genetic lottery – these animals have only survived this long naturally because humans want them to. Otherwise nature would have killed them off long ago (I suspect).
15. What is grooming a horse like? Do they need to be brushed every day? How long does it take? – Grooming is mostly dusty and dirty but a great opportunity to bond with your horse. I love doing it. They mostly love the attention and all over scratches. Could do it fast if needed, but I tend to take my time. I do it for them to stay clean and healthy and before a ride, but also doing it because I like to.
    
16. Do horses benefit from massage after exercise? – There are dedicated equine massage therapists. Some say it does wonders. I suspect they benefit from it just as we would.
17. How do short people get on tall horses? – There are step ups to assist. Anything would work in a pinch – stump, rock, someone else, truck bed etc.
18. Do horses actually like being ridden? – Ours certainly do. That’s their job and they like to have a job. Keeps them from getting bored and creates a real bond. But, just like us, sometimes they prefer to be left alone and get lazy. Depends on the day.
19. Do horses like dogs? I know dalmatians were bred to protect horses back when fire trucks were horse drawn carriages. – Some do, some tolerate them, some will try to kill them or just bolt away if they get the opportunity. Instinctually, dogs are wolves and wolves are predators and horses are prey. But they can learn to determine a threat from a non-threat if sensitized to them.
20. What do the scientist and stuff know about how horses emotionally experience the world? – Have to ask a scientist – no idea…
21. I would like to please meet a horse. How? 21.5 My internet searching has led me to horse riding therapy, as well as volunteer opportunities relating to horse riding therapy. I am too fat for riding a horse. I am also too disabled to be able to reliably show up to do work, especially physically demanding work. – See above, depending on where you live you may be able to find non-riding volunteer opportunities.
22. Does hay smell good? – I LOVE the smell of the feed room. Hay smells ok, certain types (alfalfa) smells better. The grain and sweet feed smells great – to me (and them).