We found a cute little robot on thingiverse that used a simple, yet clever locomotion system. Simple in that it used a single yellow (dual shaft) TT motor to control both sides, with the addition of only a battery and power switch.
The basic design is, as I said, clever. What could be done to expand on it? We could use two motors. A CRICKIT would provide finer, individual control of the motors. Using the Feather M0 Bluefruit with the Featherwing CRICKIT would let us drive it remotely. All this additional hardware will require the robot to be larger.
If you want to use a LiPo:
When working at your bench/desk, this wall powered supply will give you solid power and avoid issues with batteries running low.
You'll probably want to add these to the legs and body for traction and noise dampening.