Welcome, Steve, to OEM.
Can you confirm that, because the way I read your post, and even though you didn’t say it, the immersion heater (hence the iBoost) is fed off the ring main.
You’re asking for three quantities to be measured. If that’s the case, then an emonPi on its own may be no good for you, because it only measures two by directly measuring current. An optical pulse sensor might be useful, but only on the generation meter - it’s no good on the grid meter because it can’t indicate exported energy - or if it does, it can’t distinguish export and import. And it’s of limited use for indicating power (as distinct from energy) because you don’t know the pulse rate until after the next pulse has arrived!
So it comes down to where you can measure what.
Where does the PV infeed meet the rest of the house wiring? This is fairly crucial information.
What cable did you have in mind? If it’s an extended c.t. (“Clamp” appears to be a mis-translation - it’s certainly not an English term for a current transformer) cable (say 6 mm diameter ‘microphone’ cable), can you run that from your iBoost to where the meters are - presuming both grid and generation meters are together? Then an emonTx there (as Evan says) is probably the best.
But if you’re happy with a pulse sensor on the generation meter, an emonPi there (no emonBase needed now) would give you what you want.
But whatever you end up with, an emonTx can’t function completely on its own. It needs either an ESP8266 Wi-Fi module to send the data either to emoncms.org or to your own server running emonCMS, or it can use its inbuilt ISM band radio to send the data to an emonBase or emonPi, and both of those use a Raspberry Pi as a server running emonCMS.
Of course you can do it. We’re not beaten very often. Your big problem (maybe you’ve not realised it yet) is the OEM system is very flexible and that this is partly why …
There is a lot here. Just take it in steadily, and please ask if anything isn’t clear.