Great project. Before attempting to build, I'm wondering if you made any updates or enhancements?
Not sure if the original poster has.
I have built a fair few of these, because I'm running a Massoth System, a number of component changes were required because of the higher voltages, per se, they work well and have touch wood been extremely reliable.
The only change I would perhaps look at would be to exchange the Pro Mini for a Digispark ATtiny board, would make for a much smaller and compact unit.