I have done this exact job a few times now. It is nothing to be worried about. The looms are small and available separately form Autosparks. Lead times are bad at the moment (3 months?).
You could actually make a pair of harness yourself from the 2 you remove, or buy them from auto sparks for about $100 + delivery. They are simple harnesses.
Both LHD and RHS detatch with bullet connectors in front of the doors at the side of the dash. They are readily accessible and they run into the footwell and along the sills behind the sill tangs into the B-posts on either side.
They then pass through 2 rubber grommets over the rear wheel tub and into the boot.
On the LHS is a spur for the interior rear light. The connection is actually over the rear tub.
Then the rest of the wires go the the rear lights.
On the RHS is a spur for the hand brake switch. Then the loom passes through the 2 grommets behind the b- post over the wheel arch to the fuel pump (black and white wires) and the rear light unit on that side. One of them has a spur to the reversing light, the number plate lights a join together.
With the trim removed it takes about 10 minutes to pull each side and 15 minutes each side to poke the new looms through. Honestly.
Use a coathanger wire and tape.
It really is not difficult, I did one three weeks ago .
Infact I we fitted a whole loom on a crash damaged car in a morning including the dash and engine. The loom on that car was 1 year old, so in good condition.
I was cheating though! When the car was disassembled I unclipped the engine bay wires and carefully pulled them though the 3 holes (2 holes on the lhs, one for the wipers on the rhs). I unplugged the side looms from the main dash harness.Then I unbolted the the three dash panels (top removed) and extracted the whole center dash with the loom still attached and put it in a nice big box. I unplugged the other wised on the speedo/rev counter section.
It made refitting super quick as I just bolted the center section in and pulled the wires back through as per the pics I had taken on the mobile phone in my pocket.