I've now roughly placed all the components on the pcb and will work on fine adjustment and routing in the next commit. I've also migrated to KiCAD, the workflow works slightly nicer for how I work because I can just draw the schematics before actually having to worry about footprints or picking the correct part.
PID is now implemented and works as intended, the solid state relay needed a much slower carrier frequency for the PWM signal so the prescaller was set to 7. PID tuning is what needs to happen next.