All dwarf apple trees need permanent support. For a backyard orchard the simplest system is to use a single stake to support it. People use 8 foot metal t-stakes, 10 foot EMT conduit and the top rails for chain link fences with good results. You attach the leader of the tree to the stake at 3-5 points spread along the leader. You don’t support individual branches.
In commercial orchards dwarf trees are spaced 3 feet apart and rows are 13 feet apart. The target yield for each tree is about 40 lbs and the trees are trained to the tall spindle system. Tree height is kept at about 10 feet.
In a backyard orchard you can train the tree to a central leader, tall spindle and a bunch of other systems. Central leader is pretty easy and you get a traditional “tree shape” with tree spacing in the 6-10 feet range if that is what you want. Tall spindle is good as well and makes the trees easy to prune, spray and harvest. I have trees trained to tall spindle and I have 10 foot spaced trees that I originally planned to train as central leader trees but ultimately I trained the trees to the vertical axe system which is sort of a wide somewhat taller version of the tall spindle system.
I think cordons, Belgian fences and espaliers are more complicated and sacrifice yield. They work best when you have a trellis or want the trees against a wall or fence. They’re basically a good choice when you have a very narrow, long space. This system is also more vulnerable to deer damage if you have high deer pressure.
I would suggest you look at this tree calculator and play with the variables. It will show you how soil type, irrigation, rootstock, scion, and training system all interact and effect tree spacing. I don’t think you need larger rootstocks but if you have a sandy, droughty soil you may want to go with higher vigor rootstocks. Soil that is sandy loam or heavier should be fine with dwarf rootstocks. Again use the calculator below to get a feel for how all of this works.
http://fruitadvisor.info/tfruit/clements/appletreespacing.htm
Do you have any experience with fruit trees? Have you thought about diseases or insects? Certain cultivars are disease resistant but many are not. There are no apple trees that are resistant to insects especially the fruit. To protect the fruit from insects you will have to bag the apples or spray Surround ( a type of clay) or spray insecticides. We have spray guides on the site (organic and non-organic) and also charts of the disease resistance of apple cultivars see below: