I undertand. I worked with hydraulics equippments from the ships like cranes, cylinders, valves etc. This king of hydraulics We use mineral oil, but, I think you also should know the pressure that you'll have when the pump is running, because the tubes will make a little bit of restriction which can increase the pressure. In a few thrusters systems We have this oil column, and when We turn on the system, the pressure increase a little bit. In my hydraulic area, normally, when we have a small size of pump, the pressure can be highier than a big one, and the power to make it run can be small too. I suggest to descover the calculate the loss charge in all the circuit to be sure that you won't have any trouble in your electrical motor. I used to use this formula.
Sorry, because it's in Portuguese. I'm talking from Brazil. =D