I have the RED 18-50, the RED 18-85 and the Sony 18-252 lenses.
The 18-85 cannot be used handheld unless you are part cyborg. Way too front heavy.
The Sony is just ok on the shoulder but a bit slow.
The 18-50 is a great handheld lens. Focus down to 8" and f2.8
I shoot in 4K and can then punch...
I too struggled with my ideal combo.
The bottom plate and rod holders are from Berkey Systems that also supply a shoulder pad.
Attached Miller wedge plate snaps onto tripod head and is not too bad on the shoulder.
I have added an extra Hirose on the right hand side of the camera to facilitate...