It can vary, but most of the bands in the PNW (there are at least a hundred) have about 7. Three sopranos, two tenors, a baritone, and a bass, which is a huge piece of equipment. Our bass is about 8 feet long with 10 keys and stands off the ground so that you stand on a platform to play it.
The instruments are "white-keys only," though a lot now have F#s. We play mostly Zimbabwean music, either folk songs or modern compositions by the plethora of Zimbabwean and South African marimba composers. We use no music and memorize our (often drone-like repetitive) parts along with the cues and signals for the changes. Lots of fun!