With an aftermarket radio installed you will lose the date feature on your DIC and that is all. As far as chimes go you will lose them too unless you use the proper wiring harness, this depends on what features you have in your car, Onstar, Monsoon and what not. Go to crutchfield.com and use their "outfit my car" and find out what you will need.
Everything on the display will work correctly except the date, the DIC gets its information for the date from the stock radio so there is no way to keep it and have aftermarket radio too. As far as autostart, are you referring to the remote start from the key fob? If so then you should be able to keep that as well, I did in my 06. I replaced entire system, radio, amp and speakers and don't really miss the date all that much.