Only when you feel it's necessary and before shows. Personally I bathe my horses when coming out of winter, before a show or when I feel it needs to be done.
2-3 times a month so they don't lose all their natural oils
Not often! It removes all the essential oils from their coat and can make them very uncomfortable. However grooming and brushing stimulates coat health so if you have to bathe with soap more than once a month make sure to Groom often to counteract it.
i only do it before shows or once a month
I only do it before shows so 1-2 a month
I normally "bubble bathe" once or twice a month. But I rinse off after every ride and if the horse is very dirty on the legs or something I use a tad of Palmolive
You want to make sure not to do it to often, other wise it will dry your horses skin out. I typically bath my horse with soap before a show. But I would bath your horse with soap once every 1-2 months.