What's to stop you added lots of speakers using Series / Parallel wiring?

agree with above, just don't go too crazy. you only have so much power, you will only produce as much noise levels as your amp will allow - a 1000Watt am will only drive 1000watts no matter how many speakers you put on it and the more you do put in, the more power will be lost in actually moving the cones and not producing the noise. (think first law of thermodynamics which sates that energy cannot be created, only transferred - the more energy you use getting the cones to move or heat along the wires, the less energy will be transferred to sound.)

Its bad practice to connect loudspeakers in series.

The other series speaker is effectively a resistor to one speaker and this will affect the damping factor of the amplifier, which can cause degradation of the bass quality.

Yeah, you simply balance impedance. That's just the law of the land