Without seeing the stereo or the room, here goes.

You MAY be able to hookup a pair of additional speakers. Most stereo receivers have provisions for 2 pair. Most manufacturers of inexpensive stereos do not recommend more than 1 pair of speakers be hooked up.

Where to put the speakers will depend on furniture placement, room design, and aesthetics. Many people try to line up their ceiling speakers with the lighting so as to help them blend in better.

Generally, 16 gauge speaker wire will suffice. Make sure to run a separate wire from the stereo to each speaker. DO NOT run the wires in series.

Good speaker manufacturers include Speakercraft, Boston Acoustics, B&W, Paradigm, Polk Audio.