We take all kinds of horses in training. The horse does not need to be prepared in any way other than to have the vaccinations in order, both the common one against the flu and the one against herpes.
Likewise, it may be advisable to have a equine dentist to check the horse's teeth.
The course and duration are agreed with the owner along the way as it makes the most sense to make a plan once we see how the horse reacts in training.