Regarding feet, “no foot, no horse” is Gospel Truth. If a horse is trimmed to anatomical correctness for that horse then the job is done correctly. Some folks will tell you that some angle is the perfect one for all horses but that’s utter bunk. Ditto for toe length or sole depth or frog size or trim style or anything else. And, of course if you need to protect the trim after it’s done use a shoe or such other device as might be suitable in the circumstances. 
Put another way, as you ride the horse in front of you (not the one in somebody’s book or video or mind’s eye) so, too, do you trim (and, if necessary, shoe) the horse in front of you. This means you not only look at the conformation of the horse but also the environment where the horse will live and the job it will be doing. One size does NOT fit all!!!
Here is a link that is interesting. Dr. Ramey is controversial in some places but this is pretty much straight dope.
https://www.doctorramey.com/a-few-principles-of-trimming-and-shoeing/
You will note that he, in fact, has some very specific numbers. Does this contravene my thoughts, above? No, it does not. His numbers are good guidelines and you would deviate from them if, but ONLY IF, you can demonstrate that the deviation will improve both the performance of the horse and it’s comfort while performing.
Regarding saddles, a good fitter will fit horse, rider, and discipline. If they don’t do all three then they’ve only partly done their job.
This does not require a bespoke saddle for every horse and rider and use. Fit does not need to be perfect, only excellent. Horses change shape as they move, and a saddle that fit’s perfectly while standing still will, by definition, be imperfect as the horse takes their first step. The faster the horse goes, the more it changes shape. So the saddle must not just “fit” in one circumstance it must accommodate these changes. Well engineered saddles do. Cheap ones don’t. The padding system used with the saddle is part and parcel of that “accommodation” but will not remedy truly bad fit.
Horses change shape as they age. A four year old has at least two years to go before they reach their full, physical dimensions. So a saddle that is just right now won’t not be so in two or three years. Riders, too, change as they age. We sometimes forget that part!!! 
A trainer with just one saddle is deficient as a professional. Ditto for a farrier who does just one trim. Or just one type of hoof protection. The Object of the Exercise is to follow the Golden Rule of Equine Husbandry:
You give the horse what it needs, when it needs it, and in appropriate quantity and quality.
It is the needs of the horse that drive a decision, not the philosophy of any given human.
Good luck as you go forward.
G.
