Fabia I Sound System Upgrade

Currently the car has from the previous owner, a horrendous/crappy chinese type double din screen "slotted" into the dash.

Rear speakers in the parcel shelf supports are Alpine.

My guess is the front are also upgraded.

I am looking to go back to a single din unit ideally.

Also looking to re-supply the speakers and feed them from an amp.

At the rear of the car it has small speakers in the parcel shelf sides and tweeters in the rear doors (randomly no lower door speakers).

What would be the best thing to do with the rear end of the car?

I'm leaning towards 6x9s type idea but would rather stay away from this. Would the car sound weird without rear speakers if I concentrated on a decent front setup and a sub built into the side of the boot? (want to retain boot/loading access).

Cheers.

James