Scalable production setups are favouralbe in late phases of the game. However, the transport of supplies and products does not scale well. For example, additional belts are required or new train lines have to be set up.
I suggest to use a train based solution with progressiv loading of the wagons, i.e. the train is loaded stepwise from production unit to production unit. At the loadinig/unloading station next to a production facility, I use only 2 or 3 swings of every inserter to load the train. At the next station, the train is loaded/unloaded again with another 2 or 3 swings. Thus, the train collects/delivers progressively the goods station by station.
My 4 wagon trains are nuclear powered and have a cycle time of 253 ticks for a 2 swing stop and 274 ticks for 3 swing stop. For 4x12 stack inserts (stack size 12) this corresponds to a throughput of 273 items/s and 378 items/s, respectively, for an individual station. This is the equivalent of 6.8 or 9.5 blue belts. For a 100 stack size item, the train can load 4x40x100=16.000 items. Hence the total troughput of the train line is 3794 items/s, which is the equivalent of 95 blue belts. If this is not big enough, you can easily scale by adding more wagons (and engines).
At the end you loop the train line. If you need more production units, you move the loop of the train tracks and add another unit.
All stations have the same name, including the central station. 2 stops are programmed with a leave condition G=1 from the circuit network. In case of a production facility, the G signal is generated by a timer.
The video and the following image show a green circuit production.
Per unit 273 Cu and Fe plates are being processed into 356.5 green boards per second. This corresponds nicely with the loading/unloading capacity of a 3 and 2 swing unloading station, respectively. Hence, the setup scales up upto 14 production units with a consumption of 3794.5 copper plates/s.