In Maya I know how to create an in view control that has limits on how far it can move.
IE a box that can only move a distance of 1 unit in the x direction could be used as a slider controlling a blend shape.
Or limited to one unit in x and y you could now control blends for an eyebrow, up/down and in and out.
by scaling a parent to these controls you you can control the size of the control without effecting the functionality

What I would like to know is how do I set limits like this on say a null, The standard control object?

I would turn a null into a new digital asset and then promote the parameters that you wish to lock and then in the parameter section of the asset you can set the locks on the parameter range.

Another, immediate, way to do this is to drag the parameters you want in to the 3d interface and make HUD sliders.
Then RMB on them and choose the Handle Parameters. You'll see you can lock to Low and High range and set those ranges to the values you want.

I followed your suggestion and am now on the right path.
here is my first draft of the control.

It is a good start but I still need to work on it.