30 GPM at 2000 psi requires about 31 HP, so unless you have a large gas or diesel motor, you can use the pump, but will not be able to achieve the pumps full potential.
If you gear things down, you simply reduce the rpm, and increase torque.
The hyd pump is going to take so much HP to run the processor at full potential. The pump will provide enough fluid for the hyd motor, and some HP is lost there. If you decrease the load, you could reduce the volume of the pump by reducing the rpm, saving fuel and some wear and tear.
Hyd volume dictates the speed of a hyd motor, and speed of cyl movement. You will only have pressure when the cyl are providing resistance, or the hyd motor is doing work.
Work out the GPM required for all components operating at the same time, or if you time out the operation, you could minimize the volume required.
The reason that more than one pump is used, is that the more levers you activate, using one pump, the speed for everything will slow down, and if say, the hyd motor, is getting all the volume, there is less for other components. Hyd motors require a certain volume, and cyl use the fluid briefly. You could install flow dividers, so one leg of the system will always have a certain volume.