If you want on both world SQL or loud and clear some call it. Your 20T will achieve something already but you still need to save up for more to complete the system you want. You can do it in stages so that you wont be spending more of ditching the equipment you already bought when the upgrade itch bites you.

First good head unit (a must) Alpine or Pioneer with separate sub out least 4V output
Separates - mid level - Focal/Hertz/ Audio system/RE/Rainbow and many more
Good - good 4x75W channel amp - JBLGTO/Kicker/RF
Sub around 300-600WRMS - Kicker/RF punch/Hertz and many more

Use channel 1&2 of the amp for the separates then bridge the 3&4 for the sub.

later if you feel the need of upgrading to another seps maybe in the trunk for open trunk street music (the reason some want it loud and clear) use the channel 3&4 to the additional seps and buy a mono amp for your sub preferably 600-1000WRMS..

If you dont mind buying 2nd hand it can save you a lot. Just ask for a personal warranty sa seller.

Use ported box so that you can have the street bass pounding. Deadening your doors and trunk will now be important if you hear some rattles when you pump up the volume.. use quality wires since replacing wires you need to dismantle your panels and sidings..

These are just a guide for a better planning of your setup.. remember there is no perfect setup (some spend arm and leg but still needs more) it all boils down to good research and planning and audition.

Spend your 20T wisely sir and buy gears that are tested.. I suggest visit www.kotseaudioclub.com you will learn a lot and can find a good buy on the trading section... there are a lot of good and cheap audio items for sale there. Happy hunting

HTH