The changer is Alpine but is only compatible with the Renault headunit.
The door speakers & rear speakers are both 13cm, and are easily changed.
The dash tweaters need you to take the dashtop off, but probably aren't difficult to change.
If you get connects2 or autoleads adaptors, you can find connectors for some aftermarket brands to use their headunits with the steering wheel controls & dash display.
I had the connects2 setup with a Sony hu in my vee, and it worked very nicely.
Cheers.