There are many modules for Arcanum, if you don't like the story, although I don't see why. Arcanum is the "Best. Game. Ever." for me.
About horses: RR will have a 3D engine. Your party might be 4 characters or more... And will you ride horses in a dungeon? (Stalaktites [or stalagmites...lol] hurt, they're sharp).
Also, you can simply say "make RR like Arcanum but with another story" <img src="/ubbthreads/images/graemlins/winkwink.gif" alt="" />, you're still summing up Arcanum when you talk about backgrounds (can't blame you, great game). Also, if I recall correctly, you have a default character for <img src="/ubbthreads/images/graemlins/riftrunner.gif" alt="" />, you cannot chose his stats and abilities at the beginning.
Oh and: there's an "edit" button if you can find it. It might come of use, sometimes <img src="/ubbthreads/images/graemlins/smile.gif" alt="" />.
The game might force you to leave your horses out before entering a dungeon <img src="/ubbthreads/images/graemlins/tongue.gif" alt="" />
Arcanum isn't quite what I am talking about because this game they are developing is a cross between diablo and arcanum, planescape type of games which gives as a tottaly new type of rpg <img src="/ubbthreads/images/graemlins/smile.gif" alt="" /> And I liked it quite alot actually. I just think a little more rp and interactive npcs would do good <img src="/ubbthreads/images/graemlins/smile.gif" alt="" />