You can generate the coin movement operation in the air gapped machine, write it down on paper, and then use a normal, connected computer to transmit it to the network.
The private key never left the air gapped machine, with this method.
I keep getting calls from recruiters offering 30k€ in North Spain, but they are hurting, as nowadays everybody is getting better deals thanks to remote work.
>switching ISPs may throw your internal network addressing in disarray which can be either a pain or a massive problem
Those are what ULA's do. A local router that provides global addresses and ULAs solves all your problems, and that's the default behaviour of OpenWRT (and probably other routers).
If you want traffic to not leave your local network, listen to your ULA (fd00::whatever) and call it a day.