Hey fellas, I am looking for some advice for fixing up my audio.

I currently own a Mazda 3 2010 GT. Have done few customizations already and now its time to change the factory made audio system to my own.

What do you guys think about the original speakers, and the radio and CD player that it has already? Can it be any better without damaging anything else?

If so, what do you guys think I should start off with? A new radio system? new speakers? an amplifier and a sub woofer? Im not looking to bombard my car with music but some descent quality audio system that will produce good sounds and hit high ranges when needed!

Also a place where I can get it fixed! Wanna learn to fix it on my own next time!

Appreciate your time guys!
Thanks