I did this a couple years ago, and then put a larger radio in more recently (same brand, so it plugged into the same harness). Both units have (one wired, one wireless) CarPlay, which is the main reason I wanted to do it.
The first unit was a traditional double-DIN. Air vents were a problem, so I did what others have done and relocated them to the knee pads, which wasn't terribly difficult. A bigger problem was that the radio was too deep and hit the air distributor box that the old center vents connected to. I built a new box out of cardboard, hot glue, and some duct adaptors, then fiberglassed the whole thing (this was my first fiberglassing project, and it was pretty easy). I had a few weeks of fiberglass smell coming out of the vents, but it worked great.
Most of the wires you need will already be there for the old radio, and you "just" have to connect the old wires to the new harness. You may also have to run a wire to the hand park or start inhibit relay, or get a bypass kit for $10 so you can use certain features that they don't want you to do while driving, which includes things like pairing Bluetooth devices and other basic setup.
I'd also suggest getting a backup camera kit and installing that at the same time. It's really nice to have, and they're pretty cheap (like $30).
Finally, I put a capacitor on the accessory power wire to the radio. This acts as a 5 second battery that charges basically instantly. The reason for this is that it takes about 10 seconds for these head units to start up, and when you're cranking it cuts power to the radio. If you have a car that can take a few tries to start, it means that your radio isn't going to be ready until after your car is running. The capacitor lets the radio continue to have power while cranking, and without drawing precious starter power while it does so.
Here's my writeup on it, with lots of pictures:
http://www.tmproductions.com/repairs...-radio-install
The second unit I installed has a bigger screen and wireless CarPlay (I highly recommend wireless CarPlay over wired, just for the convenience). Since it's a Pioneer again, it uses the same harness, and just plugged in. The screen is separate from the main unit in this one, which wound up being important since it allowed me to mount the unit in the center stack first, reassemble the trim, and install the screen on top afterward. I couldn't get a screwdriver in for the stock mounts, so I just used some strong magnets, plus some aluminum brackets that align the screen to the main unit body. It sticks out in front of the trim, overhanging the climate controls, but it's not in the way of anything. This setup probably isn't for most people, though.
The main unit is a single-DIN height, so it can probably fit where the old radio was. The screen can be positioned in an arbitrary location, although you'll have to buy a $100 extension cable to move it an appreciable distance from the main unit. This means that if you want to avoid the air vents, you could mount the screen above them or attached to the passenger kneepad or something. Note that this radio is notably more expensive than integrated units for reasons I don't really understand.
Here's the writeup on that, which is based on the first install:
http://www.tmproductions.com/repairs...-remote-screen
Also, be aware that you'll likely have to cut up your center stack to fit a new radio. If you haven't modified yours yet, you might want to buy one of the double-DIN ones from DeLorean, as I don't believe original ones are available anymore. Mine was already cut up, so that ship had sailed by the time I did the bigger radio.
I know some people have swapped the locations of the center air vents and radio so that they can do a flip-up screen. If you do that, you'll likely be making a new air distributor box, or else modifying the original. It's probably a similar amount of work to relocating the vents to the knee pads, but it will have a more original look.
As for the head units themselves, I only have experience with Pioneer at the moment. The UI is sluggish, but once you're in CarPlay it's nice and fast. I don't know why the main UI in modern electronics like this isn't snappier, especially considering how much this thing costs. But it does the job, so I'm happy.
-- Joe