Fish fert is mostly for N and N is to induce greater vigor. When trees are small, I like to get them to size as quickly as possible but once they are bearing meaningful fruit I am careful to not overstimulate vegetative growth with excessive N- damaging fruit quality and making trees and fruit more susceptible to pest problems. Fall fertilization is not dangerous and is actually helpful to get N to the buds before mid spring and get growth to most vigorous start. It is late summer N that can sometimes postpone dormancy and hardening off that protects trees from winter damage. This danger is highly exagerated in the literature in my opinion as you get exactly the same results here when we have early summer drought and then soaking rain in mid-august. Some trees do get a late surge of vigorous growth which itself can suffer winter kill but by my observation the rest of the tree does fine. I'd be curious of the observations of others on this point. This is one of many observations I've made over the years that makes me ever vigilant to expert BS even as I continue to go to pedigreed experts for certain kinds of advice. Speaking of the advice of pedigreed experts, Cornell recommends a general application of 2 pounds N per 1,000 sq ft annually for general orchard maintenance if you are not doing a soil and tissue analysis kind of program.

You do not need to be above the tree to prune. You could have a branch that is 10' tall and cut it at 4'. You certainly wouldn't need to get on a ladder to make the 4' cut just because the branch is 10'. All the trees you mention except for the cherry, which you will probably kill doing what you want because they don't handle constant or heavy pruning well (and it sounds like you are going to cut a large central leader to make an open vase, which is why my old cherry tree split about 15 years after I had that idea), and the guava (which I just don't know about) fruit on last year's wood. Once you get your basic tree structure down your pruning will be replacing old branches when they get too big and heading back new branches to encourage fruiting and strength. You can bend the branches down to do the heading back and the branch replacement will be done at whatever level you decide your fruiting branches will come from. That level could be radiating from a central leader or it could be a system of scaffolds. I see a lot of overgrown "new wood" fruit trees and the reason is people didn't train them with the idea of branch replacement and to continue getting fruit they need to let the tree continue to get larger and larger. Let's say you decide your base will be cut at 4' and you will allow the trees to go no more than 10'. If the trees grow 12" a year or you head them back so they grow no more than 12" a year that means you will be replacing branches every 6 years. I don't know about zone 9 but 6 years is not a unmanageable branch. If it is you could decide to replace every 4 or 5 year branch and have an 8'-9' tree. If you are really stuck on having your trees only be 6' (which like I said above, there is no pruning reason to have to have them at head height to prune them since you will be removing well below the final height and can bend whips down to head them back) you would be cutting them off after every 2nd year. I'm not sure your trees would go for that, they may decide they don't have enough tree compared to root to bother trying to populate and growing tree is more important. I have a McIntosh that hates being espaliered to 5' and it's always trying to grow more tree instead of getting heavy with fruit. You may have to do some root pruning to make them satisfied with 6' of tree or do some other stress/extra dwarfing techniques to cause them to bear heavy so they don't have the energy to make more tree.

Trees can sucker, or increase production of suckers, for a number of reasons. Some sucker profusely just because that's their growth habit, some may sucker due to root disturbance, and some may sucker because of disease, decline, or physical damage. Trees respond to removing suckers in various degrees. Some do tend to eventually somewhat give up if their suckers are continually removed and as the tree matures. I've seen reports that claim that pulling suckers off, when possible, works better than cutting them. I can't remember the exact mechanism, but pulling the suckers off does something to help to reduce regrowth. Removing the suckers earlier would make this much more practicable. There are also various types of chemicals available to stop suckering. I will include a link to an example below. Here is a link that might be useful: just one example of a sucker reducing chemical

It can but seldom does, at least around here. But you need to begin dormant sprays every year when the plant is dormant. Any general garden center will have suitable products.