My main question is why more liquid would roll down a ramp faster than less for a viscosity assignment, however I would like to have a full understanding of why heavier objects would roll faster down a hill
I am answering the title:
Why do heavier objects roll faster down a hill?
The basic difference comes from the moment of inertia. In this link, an example is worked out of two identical cylinders rolling down the same incline, of the same mass M, and the same radius b, but one of them being hollow.
The acceleration of the solid mass M cylinder is (412)
The acceleration of of the hollow mass M cylinder (413)
Thus the solid one would end at the bottom first.
It is the effect of the different moment of inertia in the rotation of each cylinder.
In a general set up , a large mass would also have a larger moment of inertia due to the volume a larger mass usually takes up, and that will create accordingly a larger acceleration than for the smaller mass .
The specific cases need to be studied , volumes, densities, axis of rotation... Cylinders are easy.
My main question is why more liquid would roll down a ramp faster than less for a viscosity assignment,
you mean "for a given viscosity assignement"
This needs fluid dynamics for an answer. I would guess high viscosity would hold back the flow with respect to low viscosity, but it has nothing to do with rolling down an incline, unless turbulence is introduced.( Honey flows very slowly, a lower level sticking on the surface and then honey flows on honey.)