To answer your questions about Harry's stables @Gasp0deTheW0nderD0g ..
Does it take a lot of capital to set up or buy a training stables?
Does it take a lot of money to tent or buy an equestrian property? Yep. He won't be in leaky ramshackle stables with no acreage. His earnings will be almost solely from riding and producing horses for other people or to sell, an eventing career doesn't pay big bucks. He may have a professional sponsor or two; most likely is that he got help from family to start his yard up, although it should be self sufficient by now.
Are we talking about eventing horses or racehorses?
Eventing horses (eventers). He probably produces some that he sells as showjumpers or dressage horses occasionally, as some don't take to all 3 disciplines. Racing is an entirely separate sport and I haven't heard any mention of him or his family being involved in racing.
The horses would belong to other people who would pay an agreed fee to the trainer, I suppose.
He likely has two main sources if income from horses; people paying him to produce (ride and train) their horses, and him buying young horses to bring on in education then sell for profit.
The trainer needs enough income to pay for premises, staff, feed, veterinary costs, insurance and transport, with enough left over for his own living costs.
The owners would pay him a fee which includes stabling and training, and basic food, bedding, mucking out, handling etc. Vet costs would be paid by the owners. He will have grooms to pay, and they're likely involved in riding some of the horses but I expect he would need to do most of the riding. If he's successful, he should be riding a significant number of horses a day, and his team preparing then for him to get on and ride, one after the other, then taking them to cool down and look after when he finishes so he been very on the next one. I.e. he should in theory be working hard for long hours, and out like a light at night.
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While I'm on the subject of horses, you don't speak to clients like Alice did in the supposed riding lesson she was teaching - you can't then go and have a conversation about your choice of language and ignore the client riding away in the background, and your aunt doesn't take over your lesson half way through.
Not least because we've never heard Alice or Lillian taking their instructors qualifications, and "the stables" isn't run like a riding school, it's run like a high end livery yard and the people who keep their horses there don't want lessons from somebody unqualified, and they certainly don't want their horses being kicked and dragged about by novice riding school clients. We hear so little about lessons happening or about clients coming and going that the whole thing is just totally improbable that it's a riding school. <stamps a Dubarry-clas foot as a makeshift gavel>