We did the Hayride on 10/31 last year, so hopefully I have some answers:
1) It cost something like $15-18 per adult. I think it was $10 for kids, but I don't know what the age cutoff was, as we had 3 adults in our party. You can get the tickets at the kennel on the day you want to ride. They have a sign-up sheet with the schedule, and it's 1st come, 1st served. If there are any tickets left over, you can purchase them near Pioneer Hall that night. You can't purchase tickets in advance of the day you want to ride. I know on 10/31, there was already a small line waiting before the kennel opened.
SPOILERS BELOW
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2)The ride can be intense. The ride starts off like a standard nightime hayride, but soon you come across a spooky old man who joins the ride and tells you about Sleepy Hollow. You'll meet Ichabod, and also get VERY close to the headless horseman ... ie. the horseman will chase you down, with the horse practically breathing down the back of the carriage, and racing along the sides. Only you know your own children, but if you think the headless horseman will scare then, I'd avoid the hayride. Besides the horseman, there's a lot of spooky atmosphere, but the horseman is the only scary part, and it's more 'intense', than 'jump-out' scare.
BTW, I thought it was great. I was sceptical at first, and thought it would be geared toward the little ones, but I was pleasantly surprised.
3) The length was probably ~20 min.
4) I've never been on the regular hayride, but it probaby utiliizes some of the same route. But, with the Sleepy Hollow effects, actors, and set-pieces, it doubt it's anything like the standard hayride.
5) The Sleepy Hollow ride occurs a few nights a week, in the couple of weeks leading up to Halloween. It becomes more frequent leading up to 10/31. Check this board as Halloween gets closer, as WDW hasn't released the schedule yet. You're almost certain to catch a night they're having the ride if you're there on the dates you listed.
Hope my answers helped
