Ok, I am not very familiar with the process, but flowmeters alone (for non electrical energy/power) might not suffice, you might need pressure and/or temperature sensors also, but I assume you know this. Keep in mind also the capability of the devices to provide instantneus consumption and accumulated energy consumption and when do they flip over or zero out, and depending on the precition you are after try to decide if you need a way of syncing all your sensors to make sure you read them at the same time (or probably better said, do you have any constraints on how simultaneously do you need to read the devices, like within 10ms, within 1 second something like that)