What I recommend is that players create all the characters they want. Buy one month of game time. Log each character in to get all the character unlocks. If you can stomach walking until level 20, you can get the riding skill for free during your VIP period by taking the horse driving skill test.
Unless stated otherwise, all content in this post is My Personal Opinion.
Yes, you will have to buy the riding skill separately for each character. Or you could get your characters up to level 20 then go VIP for a month and do the quest at Hengstacer Farms for each of them and get it free.