Well, he just had Epona with the other horses. He never expected Link to be able to ride Epona since she was always so feisty with whoever tried. There's no point in keeping a horse separate if its not gonna let anyone ride anyway, just puts extra work on the owner.I also think it's strange that he allows Link to ride on Epona at all, since that's his specially trained horse for Ganondorf...
I wouldn't call that stupid, it's stereotypical minion mentality. Side with the person with the most power and he will make you more powerful than you currently are. Ingo was given Talon's position only that he would every now and again have to answer to Ganondorf. Thus the G-man's rath would rarely come into play. We must also consider that Ingo wanted the ranch to be the best of the best but couldn't do that with Talon's mentality of "as long as everyone's happy, then so am I." Working for Ganondorf gives him a great opportunity to achieve that goal as Ganondorf has resources and power(in more ways then one).I think Ingo was stupid for letting himself be used by Ganondorf in the first place. Anything else he did pales in comparison to the foolishness of betraying a kind-but-lazy master for an unforgiving one who would kill you in a heartbeat.
No, he challenges you to a race because he notices how well you ride with Epona. He knows its Ganondorf's horse, he's just overconfident in his skills.Aside from that, I don't think his actions were terribly stupid... I mean, he might not have noticed which horse you had taken until after you won the race.
To this I say that Ingo is supposed to be portrayed as misguided, not totally evil. He doesn't do these things because its simply not in him. But he's also not a nice reasonable Person. He was given power and is used to getting what he wants without having to explain it. Realizing he's not good but not totally bad either, it would stay more true to his character to have him gamble a horse that he shouldn't have and feel that he had to pay the consequences without actually having to pay the consequences. Taking it out strictly on Link with his own hands or negotiating with Link didn't cross his mind. Forcing Link to stay until Ganondorf came so he could deal with it was more his level.I honestly think it would have made more sense for Ingo to try and kill Link somehow, rather than just lock him up in an open field on a horse. Besides, how did he plan to get Epona out of there for Ganondorf? Why didn't he just demand that Link give up Epona? Why didn't he just offer rupees in exchange for the horse, or offer you another one, explaining that he already had a buyer for that horse? And then maybe lock you up in frustration once you refused, and you escape THEN. It would have made more sense if he had only planned to keep Link until he gave up Epona.