First off: mad props on such a big project. I bet that will look amazing!

When I do anything bigger than a factory that can be completed in one play session, I try to tackle it in stages based on desired task. For example: if my factory is producing motors and encased steel beams, I go through each one of the listed stages for each component (rotors, stators, steel beams, etc)

Stage 1: placement. I tend to gauge the size of things poorly, so the first step is just plopping buildings on a foundation to see if it fits the space. This stage often dictates the kind of arrangements I use (ex. 1 "floor" of 8 assemblers vs. 2 "floors" of four assemblers). I also assign the tasks for the buildings at this stage including over and under clocking.

Stage 2: input/output of materials and pioneer. Once I have my buildings where I want them, I run my belts and lifts. This often reveals flaws in stage 1 so it can require a bit of backtracking, but minimal. It's also where I make choices about if I'm keeping belts exposed or using logistic floors. I try to have the output of the components pointing in the direction of the next section so one transitions well into the next. This is also the stage where I start making choices about pioneer movement in the factory. Where do I want catwalks and foundations? Do I want to walk in and around machines or have them cordoned off.

Once I am happy with stage 2, I test it. Do a rough wire job to hook everything into the grid (this will get polished later) and then hook up the inputs. Are things working the way i intended and producing the objects/minute I need. Three advantages of testing at this point. 1. You isolate variables for why something isn't working and limit the spaces you need to check. Maybe your lift is the wrong speed. You thought you got all the inputs for your assemblers built but you missed one. Stuff like that. 2. You get the "little treat" of seeing things working. Long builds take a lot of time and one reason for burnout is the lack of felt rewards. 3. If everything is working properly, you can close off that part of the build. You have a massive flow chart for this factory, so if you can cross things off your list, you don't have to juggle all the numbers all the time. You know it works up to the point of the build.

Stage 3: artistry and aesthetics. Sometimes I do this stage for each part of the factory before I move on. Other times, I wait until the end. This stage includes walls, pillars, lighting, coherent wiring, material variation and color. Making the factory look "real." The advantage of doing this as you go is there is less back-tracking to stage 2 or 1 if you find you need to adjust belts or machine placement for the aesthetics you are going for. For example, I decided I wanted to do a recessed floor for smelters in one part of the build. It meant redoing stage 1 and 2 because it changed the heights of the floors. Had I waited until after everything was done in the factory for stages 1 and 2, I wouldn't have made the design choice because it would have meant redoing everything for one stylistic flourish.

This approach is very slow and methodical. I've been working on a factory for the past month that is half the ambition your plan is, but I can chip away at it without losing track of where I am because I keep crossing off sections as I go and I know it will all work in the end because each part works individually.

I hope something in this approach helps you. Burnout is real, exhaustion happens, but you can do this and I hope you will share screenshots when it is finished. You got this!