There are usually two solution of the problem: one is your solution: change the soil, the second (which I usually prefer) is to change the species.
Your question is very generic (on the other hand, I like to see generic answers, because it helps to see how other "gardeners" think and work.
Mountains are difficult places, because soil/rock origin varies a lot: a range of mountain usually share a common rock type, but locally (and within few feet) the rock could have different origin. Also soil depth varies a lot.
Many fruit tree doesn't care about rocks, and in any case you cannot remove rocks in such deep. Just a rocky soil has less nutrient and less water, so you should water more often and distribute fertilizer more often (still same amounts). Cherry trees have shallow roots, so they doesn't care so much. Grape vine and apples are often cultivated in rocky soils.
Changing pH and soil is often a problem, especially for trees: it is difficult and it take a lot of maintenance: pH will tend to reset (because of water flowing in and out, so it will tend again to the original pH), and also nutrients will flow away. I would have a not-rocky good soil near the trees, which helps reducing watering and fertilizing takes, but I would try not to change the pH of the soil (but maybe for few plants): too much work on long term, for a never sure outcome).
Your question 4 and 5 are too generic. Every species and varieties/cultivars have different needs. Trees could eventually find water below the surface, so you should also observe your trees to find when and how much to water. Observing wild trees also helps: get a local flora, and try to identify the trees, and which one likes dry or wet soil, which one want a acid soil and which one a higher pH. With such easy observation, you get much more information about your soil type (and maybe you will see that you have different soil types), than chemical soil analysis (which are biased on shallow depth and previous works/fertilizers on the collecting points).
[A pro tip: check our our neighbor gardens: it help you to find which trees growth well with your climate and soil]