Hi Asic,
This is not my field also, but I think that you can not use voltages below the substrate since that will forward bias the source junction diodes. You will need to reference the substrate to the lower voltage in you circuit, and then work from here.
Voltages higher than supplay is possible if you do not exceed the oxid breakdown as in clock boosters.
About this topic I know a book "Smart Power ICs", check in the Amazon site.
About trace route. Well you will need a high voltage technology so the traces will be wide. Also due to the higher currents in power circuits you will need to check the trace resistance and check the electromigration rules in the traces vias and contacts, or you circuit will fail in a short time.
I hope this can help you ...
Regards bastos