About new stock from California - your maples, if you received them before the middle of August, they will have plenty of time to adjust to your climate, time to mature and "harden off" for winter. If you purchased them after August, the trees will not have had time to adjust, they definitely will need extra protection.
Remember, you picked up a Pinus nigra - the European Black pine. It is a single flush of foliage pine for most in zone 5 and colder. It may behave differently in more mild climates, but this far north P. nigra is a single flush pine. This means discussion of the timing of techniques would be similar to what is done for Scotts Pine - P. sylvestris, and Ponderosa Pine - P. pondersosa. P. sylvestris comes from the same parts of Europe as P. nigra.
Japanese Black Pines - JBP - Pinus thunbergiana - is what many bonsai people call "black pine" - this is a different creature entirely from the European Black Pine - P. nigra. It is more of a sub-tropical pine, it regularly and reliably sends out 2 flushes of growth every year, even into zone 5, and the timing of treatments is entirely different than what you should do for P. nigra. Boon's videos are about P. thunbergiana, not P. nigra.
This confusion comes from the habit people have of using common names and not being clear on which species they are actually discussing.
Sorry if this adds more confusion, but it is not too difficult once you get the hang of it. Your tree, P. nigra, should be treated as a single flush of growth, 2 needle pine. Look for information about Scotts Pine, P. sylvestris and European Black Pine, P. nigra for tips on how to grow this. There are a lot of nice bonsai from P. nigra, but mostly on European web groups, because it is not often used in the USA.
Hope this helps.
