Mk7 (9n2)? 58 Polo

Hi, new to the forums here. I've just bought a new polo and wanna do a few bits to it.

After some information and advice really in this post, what size speakers are in the front doors? (Its a 58 plate 3dr match so elec windows if that makes any difference), i've been told they're 6.5" but just wanna double check?

Also whats the best way about getting a decent sound from the standard head unit but without spending loads? How easy are the speakers to replace?

Another question as my car doesn't have rear speakers is the wiring in place? or will that need routing through the car? and will this be easy to connect to the standard head unit? Don't really wanna replace the head unit as it'll stand out that things have been changed and i just wanna keep changes subtle if that makes any sense.

Cheers in advance

Greg