To field grow a Juniper, would I let the lowest branches and the leader grow long as sacrifices. Remove branches not part of the final design and then wire and style the trunk and keepers?
You can, but it’s better to let sacrifice branches run long and final branches be kept short.
I have several I wired everything for movement, then planted in the ground and let them grow wild. Every few years, I dig, evaluate, and prune back, then replant.
I lost 5 junipers after planting them out in the summer. This summer was exceptionally dry and I didn't take the time to water them. Nature didn't provide. It might be wise to not make the same mistake.