I have done a lot of wiring/rewiring and am in fact right in the middle of rewiring my 71 charger. This will be a long answer so I apologize up front for that.
That said here are the basic options;
1. remove the old harness, stretch it out and inspect thoroughly and repair as necessary. Many people don't like this because they state that the wiring is XX years old etc. but unless it is damaged much of the wiring is usable and fine. This does require some patience and a FSM to understand what does what and how things should be wired/terminated. You will still require the tools of the trade which are soldering iron, strippers, various crimpers and the Packard terminals. The benefit to doing this is that you know it fits the car.
2. Buy a brand new replacement OEM style harness from some place like MH. When I say "harness" this actually means "harnesses" because these cars came with a variety of harnesses such as the dash harness, engine harness, headlight harness, taillight harness, etc. This option can be very expensive up front but you get brand new essentially plug and play harness. The down side of doing this is that these cars typically had many options, mid year changes, etc. that require the new harness to be modified to work with which requires a degree of understanding of the harness and the car (obtained using the FSM).
3. Do a combination of 1 and 2, use the good parts of the original harness and replace the bad parts with a new OEM style harness. The up side here is lower cost but the down side is that the newer harness may not be an exact fit due to many issues (usually this is very minor). You still need all the tools and supplies generally but this is a lot less work.
4. Rewire the car using an aftermarket generic harness. This is a good option especially if you are restomod'ing the car wherein you have a lot of new tech such as a computer/ECU, etc. This is typically what I do and I prefer it because I am not a huge fan of how Mopar wired their cars originally and typically I am adding a number of new things which the old harnesses do not account for plus I am normally increasing the amperage I am going to push through some of he circuits significantly and lastly I want to run/terminate my wiring the way I like it. The up side of this method is that you get a completely custom electrical system suited specifically to what you want/have, the down side is that it takes a fair bit of time, all of the mentioned tools/supplies (and then some) and a thorough understanding of both electricity and how each of the systems in the car works (for example, the dome light is a negatively switched circuit verses a commonly positively switched one). With this said, IMO there is basically 2 methods used in this option:
4a. Strip all of the old wiring out, reuse the necessary plugs/connectors and wire in the new harness as per the directions provided. This will yield a very basic but functional system however it will probably not look all that great and some things may not work as designed. With this option you get rid of the bulk head fitting and close off the hole running the wires from the fuse panel to the various places and connecting them. This is what you see on many "flipper" cars where they are just trying to get them out the door.
4b. In this option you use a new after market harness to replace the factory stuff, you wire in all of the factory switches and functions and you reuse or use a new bulk head fitting and wire the car in the same manner as OEM. This is what I do and am currently doing. This method takes quite a long time and requires a high degree of understanding of how all of the systems and circuits work. The end result is that you get a completely custom yet somewhat OEM electrical system that resembles the factory harness which is what I strive to do. The method typically is not something you do once because all of the tools/supplies are extensive to do this well but for me the end result it worth it.
As to aftermarket harnesses, there are many out there ranging from the ~$100 harness off eBay to some very expensive (over $1K) systems. I personally have used a super cheap harness off of eBay and a couple of more expensive harnesses from Kwik Wire and Ron Francis. I am currently using a Kwik wire 20 circuit Mopar harness in the Charger and I really like it. I am not a fan at all of Ron Francis or Painless (Painless is good but too expensive for what you get).
Wiring is not that hard, it just take patience and some research. You do need tools and supplies as I stated but you can minimize these if you wanted to. I like tools and I have purchase a wide array of electrical tools in an effort to make life easier. I have built a wire rack, dash stand and soldering/electrical station on wheels to facilitate these efforts.
One tool you should absolutely own if you own a Mopar is a Power Probe, it will make life so much better on the electrical side of things and help you keep from burning your car down and/or smashing your head against a wall in frustration.
Another thing that I do that is VERY helpful is to build an electrical book in which I put pull out copies of the factory wiring harnesses, drawings of all of the circuits, diagrams of how all of the switches are wired, all electrical instructions that I get for whatever I put into the car, etc. This becomes my electrical "bible" and will be the go to for as long as I own the car and it will go with the car should I ever sell it.