You need to match the speaker with the amplifier. Better or worse is not the question. The question is dynamic range and the possibility of overloading the amplifier. If the amplifier is rated 4 ohms, use a 4 ohm speaker. Same for 8 ohms. Do not "mix and match".
Yes, but you won't get rated pwer. Best is to match the speaker to the amplifier.
Not really. The only possible configurations of four 4 ohm speakers is 1 ohm, 4 ohms, and 16 ohms. This will not match an 8 ohm rated amplifier. It will work, but you will not achieve rated power output, and you run the risk of damaging the amplifier.
There is neither 4 ohm nor a 8 ohm output of an amplifier. Less than 0.5 ohm is the output impedance of a loudspeaker amplifier. Scroll down to related links and look at "Voltage Bridging or impedance bridging - Zout < Zin".
Sorry, there is no amplifier with an output impedance of 4 ohm on the market. Scroll down to related links and look at "Interconnection of two audio units". Look for an amplifier and a loudspeaker.
If the amplifier is designed for an 8 ohm load, then you should use an 8 ohm load. Three 8 ohm speaker in series is 24 ohms, and in parallel they are 2.67 ohms. Neither of those is a good match for an 8 ohm rated amplifier. If you do this, you will not achieve rated power, and you may well damage the amplifier.
No. An amplifier designed for an 8 ohm load works best with an 8 ohm load. You can connect a 4 ohm load to it, but the current rating curve of the amplifier will not match the voltage rating curve, and will will not achieve rated power. Attempting to achieve rated power will result in damage to the amplifier. Look at this mathematically... If the amplifier is rated 100 watts into 8 ohms, then it can produce 28 volts doing so. It will also produce 3.5 amperes at that power. So, when we say the amplifier is rated 100 watts into 8 ohms, we mean that the amplifier is rated 28 volts or 3.5 amperes, whichever comes first. Connect a 4 ohm load to this amplifier, and 3.5 amperes will induce 14 volts and 50 watts. You cannot get 100 watts because that would require 5 amperes and 20 volts, and the amplifier cannot produce 5 amperes.
There is really no amplifier with an output of 8 ohm or 4 ohm. All loudspeaker amplifiers have an output impedance of 0.5 ohm or less. Scroll down to related links and look at "Voltage Bridging".
You will find no 4 ohm amplifier! So you will need no transformer. All audio amplifiers have output impedances of lower than 0.5 ohms. We have "impedance bridging" between amplifier and loudspeaker - no matching. Scroll down to related links and look at "impedance bridging - Wikipedia".
Yes. As long as the speaker impedance is higher than the minimum rating for the amplifier, you are OK.
The impedance of the speaker does not determine its quality. Assuming that your amplifier can drive the 4 ohm speaker, you will notice that this speaker is louder than the 8 ohm one.
You can, but its power output will be a bit higher than its 8 ohm rating.