Yes, you can have 4 or more legs, but it isn't an advantage because energy efficience, same as more than two eyes ith an mobile head don't make much sense. Nature evolution don't waste energy. Humans a very efficient runners, which can beat several animals in a hunt. In the past they made a test between an horse and an trial champion, the horse lose it. Yes it was faster as the human, but not on long distance. There are championships like Ironman and others, where are races of 500 km, a horse can't even 42 km without a break. Efficience of two legs.