A surge tank needs to be constantly full to avoid surging. A common calculation used to select the lift pump is ensuring that it flows at least half the flow rate of the main pump or pumps. We are using twin Bosch 044s as main pumps, which move 200 litres an hour each at 72psi. Feeding these will be a single Carter Black feed pump, which flows a massive 378 litres an hour at a much lower 15psi, so we are well covered.
Added filling capacity will come from plumbing the return line from the reg. back into the surge tank. When you plumb the system this way, you will also need to have a return line from the surge to the main tank, so, once the surge is full, the reg. can still do its job and regulate the fuel pressure in the rail.