I don't have enough time to go through a thorough post, but I'll try to clear what I can up.
A show miniature comes in any size up to 38". We specialize in B division which is 34-38" A division is 0-34" I'm not sure that division B is a larger division?
going by memory, the sizes most likely were a bit off in what I posted above. However, I did not say that all show-quality miniatures are under a certain size, just that many of them tend to be on the smaller size (division A) after a bit of research I actually found that they don't even use A and B classification anymore, so I correct myself in saying that 34" and lower would be "under" and 35" and higher would be "over." Anything over 38" cannot be registered, even if it is purebred. I believe I was correct in saying that division B is the larger minis though...
As for build, when I say 'others' I meant the less halter-quality miniatures. Still fully registerable, but more pony like in the way they look. (ie; larger heads, less refined looks, thicker legs, etc. I personally prefer these as they are more functional and hardy looking to me.)
Both have good conformation, but there is a hardier, pony-like look to the second mare, compared to the elegance of the first.
Whether or not a miniature should be ridden is debatable, as many people have different views. However, I do not find any reason for them to be ridden, especially if smaller than 34". The general rule for horse riding is 20% of the animal's weight. Assuming that a 34" or smaller weighs between 180 lbs and 240 lbs (all of our twenty plus miniatures fall between these two marks, although I am aware than some are heavier) that would be 36-48 lbs of weight for the average mini, including tack (miniature horse western saddles weight 10 pounds including a pad.) Perhaps in the miniature was used very lightly for a 2-3 year old, I could see it being ridden, or if was an especially hardy animal (we use two minixshetland crosses for our therapeudic program, though they stand at 40" each and weigh nearly 300 lbs)
Many miniatures do fine with normal diets, but it is still very important to regulate their weights, as founder is at high risks. Colic is a risk for any horse, I agree- and not particularely more for minis, but it is still something that needs watched, as I have heard (may not be true) that surgery can be even more high risk for them. We have had three miniatures die in the past year from Sand Colic, while all of our full sized horses have been fine.
I do not feel that I need to justify my post about dwarves, as I don't find anything wrong with it. Backyard breeding is in no way ever a good idea, and should be left to professionals in order to help lessen chances of dwarfism, mutation, etc in not only minis but large horses.
I am sorry if I provided questionable information, but I stand firm in what I believe about riding miniatures. Otherwise, I may have been wrong as I have gone mostly off of what I have learned from other miniature horse breeders, trainers, and show people. They and I can always be wrong :)