Typically one would hook up 2 - 4 speakers. But, keep the impedance correct (resistance, for lack of a more complicated definition) by wiring speakers in series and/or parallel and theoretically there is no limit to the amount of speakers, 6 - 8 should not be a problem.
You speakers will have a much more powerful depth in sound if you do that.
Yes it should be all right. Ratings for amp/speakers are approximate but as a rule it is preferable for the speaker to be rated higher than the amp.
20 watt
No, 15 watt speakers are rated far to low to be used with an external amplifier.
Yes, the speakers (150W) can handle more power than the stereo (140W) can produce. If it were the other way around (stereo more powerful than speakers), that's when you burn out your speakers.
Why do my rear speakers cut off
64 watts = 18.1 decibels. If by 'set' you mean you have two 64 watt speakers then they will create 36.2 decibels.
100
Civic Sedan/Coupe DX: No Radio, pre-wired with four speakers Civic Sedan LX: 160-watt, four speakers, CD Civic Coupe LX: 160-watt, six speakers, CD, auxiliary input jack, CD text and "welcome" screen Civic Hybrid/Sedan EX: 160-watt, six speakers, CD, auxiliary input jack Civic Hybrid/Sedan EX with navigation: 160-watt, six speakers, CD, auxiliary input jack, digital audio card reader Civic Si/Coupe EX: 350-watt, seven speakers with subwoofer, CD, auxiliary input jack, CD text and "welcome" screen Civic Si/Coupe EX with navigation: 350-watt, seven speakers with subwoofer, CD, auxiliary input jack, CD text and "welcome" screen, digital audio card reader
4" speakers
The Focal 165-CA1 are 60 watt speakers.
A 5 Watt amp powers the 4" inch integrated speakers. Distortion is estimated at 0.3% @ 1 Watt frequency response.