Getting my head around the wiring looms

[Eternal]

Hello all!

I'm having a slight brain fart at the moment and cant seem to get my head around the looms. First let me tell you what I'm going to be having on the car.

RB25DET engine (have old loom and plugs but all documents for this loom are in japanese and not 100% correct so will make a new engine loom from scratch...)
Megasquirt V3 MS3X to support 6 cyl
Megasquirt Loom
MS3X Loom
Acewell 7859 dash

So the issue i have is i have no looms at all and the car will need all wiring from scratch from car loom, engine loom, battery/starter loom, fuse box and relay stuff and dashboard and i have no clue where to start at the moment!

Do any of you guys know if there is a premade wiring kit that will save me some time that includes a fuse and relay box or if i should just wing it?

In an ideal world i would love a nice big diagram with everything on it to work from but have not found one and dont think i will! so any advice is more than welcome!

Thanks lads.

Alex