Well done you for taking the huge step forward.
What do you hope to do with a young horse, competition etc.,
Personally - had horses all my life, - I have only once had a horse 5 stage vetted and that turned out to be a disaster in more ways than one !! Since then, yes I have had a 2 stage for eyes, wind & heart, but unless the horse is over £5K value, I would not consider it.
But having said all of that, until you have gained real experience, perhaps the first time it would be a good idea.
BUT always, without question, get blood samples taken at the vetting.
Many horses have appeared quiet at that stage only to turn into raving lunatics.
If you have a blood sample that shows drugs, the horse can be returned. This can apply to a private sale, because the animal will have been misrepresented as to its character. Obviously at that stage you would be using a solicitor. There are many crooked people out there.
I would always buy direct from a breeder - perhaps an unspoilt 3 yr old, - that can start its education slowly.