Wah, the price is not bad, I think, long time never go there already.. Scare of get your car smash? The best way tint your car's windwos first, but not total black, at least it will some reflection, so other people will not notice much what is inside your car..
1. A normal sub with box will take space around 12"X5". So sur it will take out most of the space.
2. A normal 6"X9" will have a minimum input of 50watt rms and normal HU only gives you 20watt rms. If want clear sound, is better to get an amp.
3. Your statement is true on this, but not 100%. 5750 not only got 3 pre-outs, but the face plate colour also not bad. For Pioneer models, some lower end will have single colour only which cost you around 500 if mp3 included. Since now it only cost 658, why not buy it?
4. 4 way got 2 tweeter and 3 wat got 1 tweeter, this is the differrence between 2 of them.
5. Are you chinese? If yes then you can call it 'luk kap kau'. If not then you have to look it at the shop yourself and use finger language, point it...