Fixing existing engine harness or rewire from scratch?

[Minnesota]

I'm building an 87 RX-7 (turbo or N/A haven't picked an engine yet, Manual trans) from basically scratch but have most of the main harness, a hacked up dash harness and a mildly hacked up engine harness (previous owner tried doing a 2JZ swap).

my questions are:
would it be cost effective/reliable to just fix the harnesses i have (just replace the plugs and wires that were cut off), purchase another harness off ebay, classified section, etc. , or start from scratch and build a new harness (i'll elaborate on this in a second)

are new oem style plugs available for purchase or am i going to have to find some off existing harnesses?


elaboration of intent:
project goal: restoration/weekend drift car (short distance driving/track car)
what's getting deleted: Sunroof, stereo and audio wiring, electronic locks (if applicable), flip headlights (going with fixed for reliability and weight savings)
electrical skill level: surface mount soldering, fully capable with digital multi-meter, anal about perfection in finish and performance
I will be carefully removing any wiring regarding the systems i'm getting rid of to make trouble shooting easier long term. Also if i go through the effort of making a harness from scratch i will be making a couple (plug availability permitting) to make the bulk wire purchase worth it.