Speakers in a 17' SV

I was thinking about replacing all the speakers in my 2017 Altima SV. Couple of questions first tho...the rear doors do not have existing speakers. But are they wired for speakers? Or will wiring have to be done? Then also the speakers in the dash. There's the one center one and the two tweeters. The two tweeters are there, but the center speaker has nothing in it. It has a hole for a speaker, not sure if there's wiring for it, in the cover screen isn't really a screen. Does anyone else have this issue or did have this issue?