For the speaker wires themselves 18-22 gauge should be fine even smaller will work ok...I like 18-22 to ensure good power flow. If the amp is feeding a sub 18 is my choice here.
For amp power leads for an amp that small you can likely run 8 or even 10 gauge wire and be fine. Check what the amp manufacturer suggests. The size of the hookups for power on the amp can also be a clue, small hookup spots generally mean smaller wire.
You should run the same size power and ground leads.
Badly afflicted with Corvair disease and now Scionitis
Good thing the only treatment is playing with Corvairs and Scions