Another option to consider for your CU metering is using meters which emit pulses based on consumption. We got a bunch of them installed when we got the house rewired a couple of years back. There are 9 in total - lights upstairs, lights downstairs, lights kitchen, lights garage, sockets upstairs, sockets downstairs, sockets kitchen, sockets garage & cooking.
I don’t have the exact model of meter to hand, but they were something like this.
In terms of reading reading them, I use one of the USB devices mentioned here. I’m not sure if the guy behind the site is still operating, but there are presumably other versions available. The code for this device allows me to sum up readings before sending them to emonCMS for logging, so as well as the feeds above I also have things like all sockets (the sum of the 4 socket circuits), all upstairs (the sum of the 2 upstairs circuits), etc . . .
I only found out about modbus after the meters went in, but would likely have used it if I had known about it at the time.
David