I usually try out what is included with the kit and go from there. Generally softer springs and thicker oil will provide a plush ride, but will have body roll. Thinner oil and heavier springs will be more bouncy off jumps, but should hadle smooth areas at high speed well.
Most of the time you have basic 300 or 400 cps oils provided for shocks, and grease for diff. But heavy silicon oil for diff isn't provided. Best choice would be to pick 3 most common grade
3000
5000
and 7000
Most of the time thickest oil add motricity but you lose reactivity in corners.