I use the same belts for guards/handles as I do for blades. Many of the materials used for handles are very dense and tough, and often times a belt that would work on a domestic soft or hardwood, will literally "smoke" a piece of Desert Ironwood or African Blackwood.
As far as belt backings for woods/handle materials, I like the flexible backings such as "J" weights for finishings in 220 grit and finer. This allows me to flex the belt around curves, enabling me to blend things together. The very best thing to do is experiment with various belts and backing combos until you discover what works well for you.