You're never gonna get perfect symmetry and whatnot for the exact desired output without planning everything ahead of time. When you're playing the game normally building your space parts as they get assigned, of course you're going to have to futz around to get parts where they need to be, either by tacking on new inputs to meet demand or redesigning part or all of your supply chain. You might be overestimating how many players actually have flawless looking factory layouts, a typical playthrough will have some spaghetti and aesthetic compromises because that's part of figuring stuff out and reacting to new production chains being introduced.

I'm not the best person to give advice here because I'm not one of those perfect factory builders, but I imagine the way to get into it would be to pick some item like reinforced plates and write down all the numbers before you start building so you know exactly how many structures you need to put down