Stopping mid air would depend on the technology. Why would you need speed limits? Most likely it would be the speed which is more economical. Height again would depend on economics, the higher you go the cheaper it is to run. As for policing, if every car was tagged it would be exactly the same as how aircraft work. As for the risks, it all comes back to the computer. With enough sensors it can easily tell if there is anything wrong with the engine, somewhat like the *check engine* light in current cars, but far more accurate.
We wouldn't completely replace normal cars, what would be entirely pointless. I'm talking about making airplanes cheap enough and convenient enough for normal people to drive. Somewhat like how cars were for rich people, then they became more cost effective for everyone to drive. It's just we haven't really tried to do it because we are only now getting the tech and computing power to do it.
As for the AI connect, what do you think autopilot is doing in aircraft? AIs are really good at controlling these types of things. The reaction time is far quicker than any human could hope to have. AIs are predictable too.
Self-Driving Car Test: Steve Mahan - YouTube
As for being hacked... Simply don't allow outside networks to send code which is run.