As the planting gets older it will become necessary to thin out the limbs. Don't begin to thin out the bottom of the tree until fruit is higher in the tree. Remember that fruit controls growth, whereas, pruning encourages growth. You must have abundant fruit present or regrowth will be tremendous and costly. At maturity, summer pruning may be required for some cultivars where the uprights are removed to allow for greater light exposure.
Fruit also controls tree height.
The VA system should not be headed until fruit is at the top of the tree, and the leader has been pulled down with the weight of the fruit. At this point, perhaps year 5 or beyond, the top can be reduced in size to allow better light exposure to the lower limbs. There are many different kinds of trellis systems being used world wide. Some are extremely formal in design and require detailed timely management. Trellis systems involve the positioning of limbs along the supporting wires.