I only see one option, horse for animal companion, for Arcane Rider human. Is that normal?

Yeah, sadly. They used to get access to all animal companions as possible mounts and got bonkers powerful if you picked the smilodon. Some patches back they limited them to the horse. Still a good class in my opinion though. And mounted combat is some of the best fun I can have in this game.

what should i set the horse to? Wrecker Bulwark, Racer?
I set the Human to Mostly dexterity and intelligence and gave it weapon finesse feat to have attacks work off dexterity. Not sure which to pick for the horse though. There is different endings right? So i can try different character builds.

Bulwark is generally the way to go for your horse. Build them up to be a tank, and then whenever you are riding it, you get the the mount's ac and not your own.