Short answers, pulled from the story.
The Icelandic horse performs five gaits: walk, trot, canter/gallop, the tölt, and the flying pace. Breed registries count the canter and gallop as one gait, making the total five rather than six. The tölt is a four-beat lateral ambling gait; the flying pace, or skeið, is a two-beat gait with a moment of suspension between footfalls, capable of reaching up to 30 mph.
Icelandic horses are always described as horses in breed registries, even though they are often pony-sized. Theories cited for this distinction include the breed's spirited temperament compared with other small breeds and its weight-carrying abilities, which more closely resemble those of a full-sized horse than a pony.
Icelandic horses are notably long-lived; a mare living in Denmark reached the age of 56, and another in Great Britain reached 42. The breed's most productive years fall between eight and eighteen, and both sexes remain fit for breeding until age 25.
Iceland's parliament, the Althing, passed laws banning all future horse imports in 982 AD, after attempts to introduce eastern blood into the Icelandic line caused the stock to degenerate. The breed has developed without outside influence ever since.
The 1783 eruption of Lakagígar killed roughly 70% of all horses in Iceland. The eruption lasted eight months, covered hundreds of square miles of land with lava, and rerouted or dried up several rivers. Volcanic ash poisoning and the starvation that followed caused most of the deaths.
WorldFengur is the official international studbook for Icelandic horses, launched in 2000 by the International Federation of Icelandic Horse Associations and the Icelandic government. It is a web database tracking pedigree, breeder, owner, offspring, photographs, and breeding evaluations for each registered animal. Around 300,000 Icelandic horses, living and dead, have been registered since its inception.