AD characters as Horses:

Toby: Akhal-Teke - hardy enough to handle deserts, resilient, high endurance, fast and agile, spirited temperament

Rick: Pintabian (pinto/Arabian) - high stamina, friendly nature OR Spanish Barb - great stamina/endurance, eager to learn/please, hardy, can handle harsh desert terrain

Charlie: Tersk - refined and smart, can be spirited

Ben: Andalusian - wide chest, stately appearance, graceful, agile, moves quickly and accurately

Kylo: Arabian - fast, high stamina, spirited, expressive eyes

Paul: American Warmblood - friendly, calm, good intuition

Phillip: Morgan - strong, proud air, well-defined lines, attractive, showy OR Tennesse Walking Horse - tall, handsome, showy, quick turns, flowing motion

Flip: American Standardbred - good in a harness, calm, good-natured, adaptable

Al: Quarter Horse - long-legged, hardy, quick, hard-working, tough

Clyde: Clydesdale - graceful, tall, long legs, docile OR Shire - known as a Gentle Giant, calm, easy-going, hard-working, glossy mane

Ronnie: Irish Draft - used as a police horse, keep their cool in noisy environments, resilient, powerful build, docile

Jamie: Hackney - showy, brings attention to itself (this was a bit of a stretch but the 'Hack' part made me think of Jamie)

Paterson: Paso Fino - smooth gait/ride for passengers, very gentle

Sackler: Thoroughbred - athletic, spirited, determined, high energy

And the man himself, Adam: Friesian - sturdy, muscular body, wavy flowing mane, proud carriage, mostly docile