For Horse ;
1) make or find a 3d texture for horse and create a new root template id with necassery tags and set faction as netural.
2) make the character stats for horse you created in template ( you can add a high speed stat)
3)Modify any trader which you want to buy it from with a story dialog and buy horse for gold dialog.If player have enough gold then a horse will be spawned near you with story scripting you can add it to your party.
4)When you owned the horse with char script if you click on horse then you can call behavior function sit with little asset change for full visual compatibility. Then you can ride your horse. Even you can put your horse some fighting skills too
I will think it