Instead of running 1 pump/motor for 3 functions, would it be better to run 3 smaller pumps/motor for ex.
 

Instead of running 1 pump/motor for 3 functions, would it be better to run 3 smaller pumps/motors and individual valves for an excavator? That way each function (stick, boom, and bucket) can get a dedicated pump?

Re: Instead of running 1 pump/motor for 3 functions, would it be better to run 3 smaller pumps/motor for
 

Pumps, motors, and electronic speed controllers to run them are expensive and having multiple pumps would add unnecessary complexity, more expense, and require more room inside the model. One good pump and motor combination, with high flow, will handle anything you think you might need. Buy a good one, and you'll be set.

The only application I can think of, where a second pump might be beneficial, is for a hydrostatic drivetrain, where the wheels or tracks are driven by a hydraulic motor. Then it might be advantageous to keep the pumps separate. The model would be more powerful that way and the drivetrain hydraulic flow needs would not steal flow from the boom, loader, or bucket functions. You really don't see many hydrostatic drive models though. Damtiz excavators are the only ones I've seen that use hydraulic track drive motors, and that's not a continuous duty application. Electric gearhead motors would be more powerful than small hydraulic motors anyway, until you get into the very large construction models, which are mostly scratchbuilt and not readily available anyway. In those cases, pumps could be easily upsized to run all hydraulic functions without the need for a second pump anyway.