If you do decide to get an aftermarket headunit. I would stick to single din (as said before, much better value for money. Double din tends to be mainly wank factor, unless you want dvd..) and get a fascia kit.

What single din you want is up to you. If you plan to put amps and stuff in eventually, get one with at least 2 pre-outs.. if not, 1 pre-out will suffice. And usb and aux depending on what you want...

But anyway, for now, they aux kit will be fine. Go with that