I doubt we will have a garage to customize horses or anything like that lol.
At best they can make it like in TESIV where every horse color had a meaning. And maybe make it so that horses with no equipment (however the chair is called in english) are usable but easy off balanced, and that you have to pay for chairs for two men?
I think most of the money could be spent on properties, clothing and weaponry but certainly not transportation. Sure, they could throw in a paid 1908 Ford T but that would make little to no sense to have. My guess is that they will make some gang system and you have to fight for the control of a town and then invest some resources to upgrade that town idk. Like TESO or Pokemon Go.