Well the choice is yours. If you have some free time, curiosity and willingness to finish it, then you can count to get some help here from me and hopefully from the others too. I see two problems from my side:
1. I am not sure that my experience is enough to help.
2. My free time will be very limited in the next two weeks. Most likely I will be able only on late evenings and not each day.
Still I think it is worth to try, because it seems to me, that you are near the finish line.
Speaking about you have discovered. It can't be permissions problem for now, because domoticz daemon is running with root privileges and it has full access to system.
I would read this Rene (Chimit) comment very carefully:
Besides that, Domoticz also stops reading the P1 meter if another process reads the same port at the same time. Even if just once (for testing or something). Domoticz needs to be restarted after that to allow for collecting data anew.
Does it nothing reminds to you?
sh /ffp/start/domoticz.sh restart
to restart domoticz daemon service.