What do I need for a proper under-dash rewire?

I need some help determining what I need/what route to take with patching up the under dash wiring on my '68 notchback Barracuda. I drove it while I was home for Thanksgiving, and while investigating why my turn signals, aftermarket tach, and blower motor were intermittently shutting off, I discovered that the wiring under my dash is a good bit messier than I thought. Dangling connectors, wire screws, wires just straight up tied together next to insulation... It's a bit of a miracle this car hasn't caught fire.

I've already been planning to pull the cluster to repair some things behind it, but now I'm realizing that I should definitely do a complete rewire or at least patch things together. I can't afford a $600 brand new under dash harness, so what would you all suggest I get in order to do a good, solid repair/rewire job? I know how to solder properly and whatnot, I actually love wiring and electricity, but I just lack exoeriexpe. Should I get a bunch of colored wire or reuse/repair the factory stuff? What tools for crimping and splicing do you suggest? Anything I should know about dash wiring that would be good to be aware of on a '68 notch?

If it helps any, the car is a 1968 Barracuda notchback, factory 318 car (now has 360/904), no A/C, 3-speed wipers, manual steering and brakes, suspected to have had a map light switch during it's life (now missing), nothing special in terms of rear defogger or fancy options.