[Bonzabonz]

Datasheets are a great place to start in order to judge current needs of a particular component. Most motor datasheets I've seen list a free current draw and a stall current draw. Even though the actual current draw will vary from application to application (load on motor, speed, input voltage from speed controller, etc.) those measurements will give you a good place to start, and can be used to get a rough estimate.

As far as other components go, like the control system, the current draw listed in a datasheet is generally pretty reliable - assuming you can find the correct datasheet. IMO it is generally safe to assume that an individual component from the control system wont draw more than a couple amps at max.