On the question of the 3 phase metering… all meters will meter across all 3 phases for import, but not for export. The term to google is ‘polyphase metering’
Example - you generate 3K on 1 phase and pull 1Kw from each of the remaining phases - without a polyphase meter you will be PAYING for that 2Kw. With a polyphase meter you will not be.
All SMET2 meters (latest smart meters) are polyphase and net the generation regardless of phase. My older (5yrs) non-smart was not and was silently hurting my wallet when I found this out.
For my 3 phase incoming / out going metering, I look only at the total KW, I do not look per phase. This is easy for me as I have a Socomec Dirus A40 power meter hooked up on the utility talking to emonCMS via modbus, so I know my data is accurate (and the meter also deals with import/export properly).