I did my heater core 6 months ago, it wasn't all that bad. There are a few good write ups you can find online.
TJ Heater Core Replacement - 1
The only real problem was trying to take apart the ac lines, the write up was not to clear on that, you need a special tool that costs about 4 bucks lol. Yes you do need to take the whole dash out and it only comes out as one piece. Make sure you disconnect the battery and open the doors all the way (take off door straps) to make it easier to take out, and get a second person to help you lift the dash out, with two airbags it was a bit awkward doing it my self.
Take a bunch of pictures so you can remember how it all goes back. You will need to discharge your ac system at a shop as per state laws, then recharge it when you are done. (do not run your ac until it has been recharged). I'll keep an eye on this thread since my mom was born in Dover