1) My plan is to simply run old versions of the operating system, supported by disk clones made using tools like Carbon Copy Cloner. I currently keep an os 10.9 system running this way, and a 10.14 system in a dual boot capability presently. Perhaps in future I will have a triple boot setup, not looking forward to that.
2) Time machine does not like to restore to an older os version so I use both Time Machine in conjunction with a hot-spare disk clone. Rsync is also able to maintain the freshness of these backups if Carbon Copy Cloner not suitable.
3) I can't see why it wouldn't be possible to convert 32-bit x86 machine code into super ugly 64-bit x86 machine code. After all, doesn't the x64 support 32-bit multiply? Sure it does! A processor supporting x86-64 still powers on in real mode for full backward compatibility, as x86 processors have done since the 80286. x86_64 introduces two new modes of operation, 64-bit mode and compatibility mode, along with a new 4-level paging mode. A chip series called Itanium was invented to attempt at a pure 64 bit architecture. In January 2019, Intel announced that Itanium 3 would be discontinued, with a last order date of January 2020.