Thank you for the reply! I’m always a little nervous to cut too far back as been told that Junipers wont grow if you cut past green. Is this accurate?
Correct that cutting right down to bare wood is likely to stop growth on that section BUT if you cut back hard and leaves some green junipers are quite likely to develop new shoots along bare sections below. Reduction can be done but needs to be done slowly over several years.
Most of the branches I'm looking at in the picture have shoots all along so should be no problem cutting those shorter but as I said earlier not this winter. Wait for next spring when it has recovered from the first trim.
Treat shimpaku as other junipers. Outside is best but you must water correctly to match outside heat and drying winds to keep them alive. Correct watering is one of the hardest things to learn.
Grow junipers on in larger containers is a great plan. I have lots developing here in pots. Sacrifice branches are a great way to thicken lower trunks while not letting the main trunk get too long.
Blue lines show the real bonsai trunk. White shows where I will convert the sacrifice branches to jins.
I wire and bend young trunks while they are still flexible as bending later is really difficult then allow them to grow and thicken. Look at the bends and curves in the trees shown above.
Most bonsai are developed by grow and chop and junipers are no exception. Some parts will grow long but will later be chopped off completely or turned into dead wood 'jin' Having some lower branches to cut back to and use them to develop a new trunk and branches is the key to most bonsai development so, no, the size is not set once you remove the tree from the grow pot.