Usually one would choose and spot near a branch that could be easily wired upright. Prettu much can chop most anytime here. We usually chop just as the buds show green.
That’s a good question that depends on three things, growth rate, desired height and design. The idea is to create taper… but this depends on which design one wants.
For a tapered upright, one might cut lower and more often. For other designs, lightening struck, split trunk, stump (takes a long time, best to but this, etc this is not the case.
The very fastest way to grow these trees out is in the ground… flat out. The next best way is to up pot every year, which is what we do. Anderson flat for this tree might work for a couple years to start with, then not so much.
A good nursery soil with a pumice drain layer seems to be the best Gro mix for in the pot/flat here. ( we’ve 1 Dawn and 3 coast redwoods growing out). If in bonsai soil the tree will go dry fast, so best to stick pot in a tray of water.
That’s all I’ve got! Good Luck and keep us posted.
cheers
DSD sends