Get a pac interface. It will allow your OEM controls to work nearly every aftermarket radio out there.
As for a navi, I have an avic d3. It's a little dated now, but I love it. I have nearly every ad-on available for it, and it's got to be the best mod I've done. Bluetooth, navi (that never loses your route-it connects directly to your VSS so even if it loses signal, it ALWAYS knows where you are), XM, sirius, USB, and IPOD control. I can't speak highly enough. And if you decide to upgrade eventually, all the ad on modules will work on any pioneer with an IP-bus connection.