Well you don't need a whole lot of ray trace bounces unless you have reflective things, for one, and pixel samples can be adjusted as well as min. shading rate.
Unless you have a bunch of mirrors and reflection and refraction, you could get away with only 1 raytrace bounce. If you have anything reflective in your scene, you will need more than that, maybe 4 or 6 bounces. And that will need to vary if you have refraction, too.

The bucket size determines how much RAM is allotted to each bucket. Larger bucket sizes seem to render more quickly, but a lower bucket size is better if you don't have a lot of system RAM.