This is a straightforward fluid flow problem. It just needs to be solved in a series of steps. If, of course, I properly understand the OP. The sketch below shows what I think the OP is trying to do.
Step 1: The OP needs to confirm that the above sketch is correct. If not, a correct sketch needs to be posted.
Step 2: The vacuum at P3 needs to be sufficient to lift the oil to that point, plus a little more to make the oil flow. It's a simple calculation involving the lift distance, the specific gravity of the oil, and the pressure drop of the oil at the desired flow rate. The air flow through the last hose is low enough that it can be considered to be zero.
Step 3: Given the vacuum in the header, and the length and diameter of the hoses, the air flow through the open hoses can be calculated. This will be a stepwise, iterative calculation because the pressure drop is more than 10% of the atmospheric pressure.
Step 4: Sum the airflow through the 11 open hoses. Size the header so that P2 is only slightly higher vacuum than P3.
Step 5: I'm assuming some sort of oil separator before the vacuum pump. That's the box between P1 and P2. Any oil separator will have a pressure drop. That pressure drop will further increase the vacuum at P1. Note that ACFM (Actual Cubic Feet per Minute) increases as the vacuum increases, so the ACFM at P1 will be greater than the ACFM at P2. Note that P1 should properly be shown at the pump inlet because you need the vacuum and ACFM at the pump inlet.
Step 6: Go back and double check your work. It is very easy to mess up calculations by not keeping proper track of vacuum vs absolute pressure. All flow calculations are done using absolute pressure, then converted to vacuum. You need to include your altitude above sea level because 1000 feet altitude is one inch mercury vacuum is about 0.5 PSI. That becomes significant at the vacuum in your system.
Step 7: You now have the atmospheric pressure, the vacuum at the inlet of the vacuum pump, and the flow rate in ACFM at the pump inlet. If there is a filter or silencer at the pump outlet, that flow restriction must be included in the system design. You now have the information to size a vacuum pump and oil separator.