For those using the official 7" display you can use MMM-Screendimmer
Or write directly to /sys/class/backlight/rpi_backlight/brightness
I don’t have any ideas for you, except to say that I never even thought about trying this - I’m going to try it on my Samsung tv!
I would reduce the config down to the default, and then eliminate modules to see if anything works.
I’m terrible with the soldering iron but here is what I did
I used a 12v 5a power supply with the same board - you don’t have to stick with 3a, that’s a minimum recommendation for the controller. So getting a 5a power supply should cover easily the controller and the rpi.
In the spec sheet you posted, see where it says CN3 on page 4 &5. This is an optional connector that may (or may not) be on the board.
Pins 3 & 4 are 5v and 5 & 6 are GND.
Note, however, unless you want to do some simple PCB soldering this isn’t the way to go. What I did was attach some header pins to the board, cut one end off a USB cable and attached it to the pins, then plugged it in the normal way into the RPi.
I wrote one for pulling data from the Enphase Envoy-C (directly, but only ones with old firmware). There is also one for pulling from Enphase Enlighten API (couldn’t get an API key for reasons to date I can’t figure out)
I also believe there is one for PVOutput.
You may also find an openHAB plugin exists for your system, and then you can use MMM-Openhab.
My MMM-EnphaseEnvoy module could easily be modified to fetch data from other sources if you want very simple display - it is limited to current power, generated today, this week, and lifetime.
Supplies 5v on the CN3 pins (probably headless on the board, but 5v is there)
This guy says it’s good up to 1.5 amps (https://www.raspberrypi.org/forums/viewtopic.php?t=67312)
I’ve confirmed that this is there and can indeed power the rpi - however, you if you need to power USB devices from the pi, it may not be enough.
Depending on which controller board you actually end up with (sometimes ebay gives out different ones) - the controller itself may have a 5v output already on it that you can use.