Do you have a tablet you'd be willing to use? A tablet like that will set you back about 500 bucks, and if you wanted one to work with navigation you'd probably need one of about 600 dollars at least. They're nice, but i'd be terrified of someone breaking into my car to get it so just make sure you put it away after every drive. I don't see how it'd be too hard to make the dock, you probably just have to find the dock for whatever tablet you want, and then just modify the dock to make it able to attach to the car. I'm not honestly sure about the bluetooth though. If someone made a call to you I doubt you could use the tablet to answer the phone and stuff. Would you keep the original radio?
Honestly I would just invest in a nice touch screen headunit. I know it'll probably be around 900-1000 dollars for a somewhat decent headunit with these features, but it's definitely worth it IMO. Hope this kind of helps!
I forgot to mention, if you wanted to use it's navigation like I said it's probably another 100 dollars to get a tablet with 4g also. and then you're also looking at extra cell phone service payments to have the 4g on it. Not worth it imo.