No thats exactly how i have them setup, same wireing as the starlet graced my hands with ..
Dont buy sony tho, there shite haha! - Im also looking for some, what do you plan to get?
An Amp isnt needed no, but if you do add one into the setup, it sound's sooooo much nicer. That way you can get a sub aswell (nothing too big is needed unless your the kinda person that likes to show off). I found when I ran 2 speakers up front and the 2 6x9's on the parcel shelf, without the Amp the headunit struggled on some songs at higher volumes. You'll find this out yourself though and if you feel the need for an Amp, it really isnt a hard job to install.