6x9's and 7x10's are confused little speakers, don't know if it's a sub-woofer, a mid range or top end speaker. Useless as any of those, split system blow them out of the water at mid and low range and sub-woofers absolutely destroy them at low end.
As said by others, splits front and rear, sub in the back.
The I have lots of money system:
My split system suggestion: Infinity Kappa/Kappa Perfect's, JBL 660GTi, Boston Acoustics Pro series. There are others, just can't think of any now
My sub-woofer suggestion: JL (Sorry I'm biased, JL all the way)
Amplifier suggestion: Rockford Fosgate
The I don't have lots of money system:
Split systems: Infinity Kappa, Kenwood, Rockford Fosgate, JBL (rather still get some decent split systems because it makes the biggest difference IMHO)
Sub-woofer: Pioneer Premier/Kicker/JBL
Amplifier: ?? Whatever works for the chosen configuration
My setup recommendations:
A single amplifier, 4 channel, highly recommended that it is 1 ohm stable, run front and rear split systems in parallel from a single channel pair and the sub-woofer from the other channel in bridged mode.
Since you have a hatchback you may want to look into a shallow mount sub (I know boot space can be a precious commodity in hatches), Pioneer Premier has a decent looking shallow mount sub considering the price, JL has a really decent on but it's probably gonna be hellishly expensive. Also create a custom enclosure, sealed, if you buy JL, Pioneer and JBL (only brands I've actually personally owned so far) they give you a sheet with the optimal enclosure size. You just need to buy the wood and make it, considering that most places will gladly cut a wood panel for you if you buy there it's hardly difficult to create a sealed sub-woofer enclosure.
Run a single 0 or 2 gauge wire from the battery to the amp (rather go big and get the hassle over with), upgrade alternator ground + positive wire (between the alternator and battery), battery ground and engine ground to 0 gauge (or 2 gauge). If the car is already running 0 gauge or 2 gauge you only need to upgrade if the head lights dim. I've used standard wire I buy from weld store in Pretoria for every installation so far, never had trouble, plus it's much cheaper than others. Still 0 gauge is like R30 a meter. Cable must be stranded wire!
One of my previous cars was a Corsa Sedan with 2x Amplifiers, when the sound was at it's loudest the headlights dimmed lots and the revs kept dropping (normal idle is at 800rpm and it dropped down to 500rpm on bass hits). In the end the coil pack went and the ECU voltage regulators weren't doing too well either (the sensors are supposed to run from a 5volt reference which at the end sat at 4.94 volt, doesn't sound like much but for a voltage reference that is SERIOUSLY inaccurate). So rather upgrade those ground wires if you have head light dimming and you care about the state of your cars electrical system.