Every centrifuge or assembling machine are connected to a central belt with a splitter. This make it easily expandable as you only need to extand the central belt if you want to add any module.
The centrifuges with Uranium Processing have two design, one classic and one with a buffer chest wich help to autostart the sytem.
You need to have the Nuclear fuel reprocessing with an input priority and before the Uranium fuel cell production otherwise not enough used cell will be reprocess and will block the nuclears reactors.
It's better to have the Kovarex enrichment process with an output priority and after the Uranium Processing because to start the system, you want the Uranium-235 to go in priority to the Kovarex enrichment process.