This tree is niwaki not bonsai. Multi-trunk especially for pine falls more in the advanced skill group. Try keeping it alive first, that's halfway to winning the battle. In Germany, the winters are too cold so I wouldn't do major autumn work.
Winter is busy here.....repot time for pines and fruit trees, mind you the fruit trees are in cold greenhouses and the pines are thawed for two or three days before they can be repotted. Hahaha In Korea and Japan winter is a busy season.
Here's a native. Yamadori yes actual yamadori Hinoki from private land on Halla Mountain. Collected in March. Left to recover. First wiring here which is slapdash as I only had an hour....
The things I do for you people..... will be my tree unless someone buys it......
Inorganic I meant sorry typo. They will be fine. Their natural range (China, Korea, Japan) gets to those temps. As long as they have airflow they are fine