You will also need the antenna adapter. As far as speakers go, heres what I suggest. Swap out head unit first, since you have no desire to amp your speakers, or get involved with any other add-ons, listen to your factory speakers with your new head unit. You may actually be surprised, and be satisfied with the difference the new head unit alone makes. If not, then move on to the speakers.
If you do get to that point, I would suggest (if only to simplify for you) Just changing the woofers in the doors to something that has a little more midbass output, Like the CDT ES-L6, and leave your dash tweeters in. Changing the dash tweeters without a proper crossover network is not going to gain you a whole lot in terms of value per $$.
In the perfect world I would tell you to get a component set, but what I have described IMHO would be your best route at this time.