Re. soldering magnets - I’ve heard that having a big magnet with a thin piece of silicone rubber on top helps.
The idea is that you take the small magnet you’re soldering and lay it on the big magnet with the silicone rubber in between, then solder. As the small magnet cools, the field of the big one remagnetises it. The silicone rubber stops the heat reaching the big magnet to demagnetise it.
Anyone know if that works?