so with a bit of digging through the graves and found this
Replacing Td5 fuel pump with Bosch 044 inline pump
so it looks like you are correct in that the low pressure does feed the high pressure after going through the filter, then the fuel coming back from the engine looks like it goes through the filter as well.
and ill probably add a fuel cooler after the std fuel cooler just to help lower temps as while it is bring the fuel back from probably around 150degC to 70 if i can get it down to 10degC above ambient that would be even better