Hey man. Welcome to the forum. Perhaps you could give us a little more in depth info on you plans rather than just a drawing and some loose ideas.
Firstly, DO NOT CUT THE SPRINGS. If you want to get defected go ahead, otherwise lower it properly with shorter shocks and springs. Cut springs = deathtrap.
Secondly, T20 is dark enough. I had T20 on my old car and you couldnt see a thing inside it. Besides, I reckon two different darknesses of tint would look a little funny. (on anything else other than say a Ford Courier...)
Thirdly. Sony Xplode should be avoided like the plauge. Save your money and get a decent brand. The extra time you may have to wait to save up will be well worth the extra quality of sound and longevity of your speakers.
Fourthly. Try and get the rear speakers closer to where people are sitting. Most times in a wagon, when people put the speakers too far back it ends up sounding a little funny, and you will generally ruin the speakers quicker because you have to turn them up louder to hear them.
Fithly. Get some rimzzzz... Wheels make the car and provided you pick some nice ones, (not the Bob Jane $900 specials) you will have a nice indiviual look to your car that you can always claim as your own, rather than something you saw in hot-fulli-sic-fours magazines.
Cheers. And good luck with the car.