it sounds like the new harness is pretty easy to follow along for what wire goes where. bonus. I have seen some guys sell the project because the wiring got started and got too deep for the owner. once wiring is started a lot of shops won't want to take over and continue with that particular harness because they have to warranty their work on stuff they don't have history with.
after having wired a lot of things from scratch I can say you may want to invest in some of those velcro release cable ties. it helps to bundle a harness together so you can easily add a new wire to the bundle without undoing tape or doing an estimated length but then finding out you were too long or short. when done they can be removed after taping the harness in a few spots (or fully) and then running the wires in a loom of some sort before clamping them down to something. if using the plastic split loom there are tools made to help you get the wires inside the split loom as well.
here is a link so you can see what the tool looks like and how it works
https://www.cablesnmore.com/split-lo...tallation-tool
https://nickstruckparts.com/products...plit-loom-tool
there are also different options for loom you may not be aware of as well as clamp styles, tools, fuses, relays, pigtails, connectors, tech articles, etc, etc, which this link shows. check their home page for a drop down
https://www.wiringdepot.com/store/c/...Wire-Loom.aspx
there are also lots of split loom fittings available to make your life easier and help you make a proffessional looking job
https://www.wireloomtubing.com/plastic-conduit