I guess that you by "a single board" means an SBC (Single Board Computer), as you'll need a board for whatever microcontroller you may choose.
A certain size of (modern) microcontroller can hold more than the SBC's of "yesterday" and the SBC's of today can be counted in PC-104's and the ITX family (complete PC's in very small sizes) , which you don't need.
Microcontrollers comes in a wide variety of sizes and clock speeds, from a few MHz to several hundred MHz.
I'm not sure what you're hoping to gain from using several accelerometers?
A single one and some flex sensors should be adequate, better top off with a gyro, if you want to go all out.