@mickles From the schematic R5 would appear to add a fixed 500uA to 5v current draw. It is used to turn the MOSFET Q2 on when only being powered by a lipo cell. So in theory you could change it to a higher value or remove it altogether if never using a cell.
The TP4056 charger is also specified to take around 100uA in standby, again if never using a cell you could disconnect it.
The CP2104 is likely to amount to about 200uA in standby. I assume the function of the Q1 and the current mirror is to disconnect the Vbus rail from the 5v supply when powering from the 5V pin. I think this will ensure the CP2104 realises it is not connected to the USB and go into standby, also it will disconnect the usb pullup resister saving more current.
Anyone else have any ideas about the current mirror, I'm not sure how much current it actually uses ?