I always jumped as a kid because that's what I was exposed to was jumping. I started taking dressage lessons when a coach started coming to the barn I was at around age 9 and was hooked. I still jump, very occasionally, but focus mainly on dressage now. A few horses I have ridden I have shown also in the hunters and eventing, but I now show almost exclusively dressage, and did my first international competition this year.
I ride 6 days a week, and I go to the gym, do yoga, go on a bike ride/run, etc.. at least 5 times a week to stay fit. I am hoping to start riding more horses soon, and I want to drop my ammy status next year, as well as apply for a judging card.
My advice to anyone starting in dressage is to find the right coach!! A good coach won't care what horse you're on as long as it's sound and will teach you in whatever tack you show up in as long as it fits. I know many people who have gotten into dressage taking lessons on their half arabian horses while riding in western tack with a dressage coach. The tack and the breed of the horse is secondary to the training.
They say money doesn't buy happiness -- well happiness doesn't buy horses!