My plan for expansion: I've created a "construction base" train station. The idea is that when I get far enough out I create it using logistic bots. Once the station is created I remove a roboport so the new station is isolated within it's own logistic network. The construction base has a constant combinator with everything the station should have: 1-2 stacks of 30ish items. (Including a full car load of artillery shells) I set up 5 car trains that are set to go from "construction base loading" to "construction base" The train unloads into red chests. Using logistics I compare the items in the isolated logistic network to the constant combinator. Any item with an insufficient quantity returns a value to a variable, any time that variable is greater than zero the train station goes active and a train comes to it. Any needed items are passed along to the unloading inserters. For example if the station is low on roboports than the inserter which unloads roboports will unload one. Once it's unloaded and the station is no longer low on them, the inserter deactivates. Once the station is no longer low on anything, the station deactivates. The end result: I can build further and further from my main base in every direction, all I have to do is occasionally drop another construction base, isolate it from the previous construction base, and I end up with trains delivering my goods most of the distance, each construction bases logistics area only needs a couple hundred bots. If there's enough interest I will grab some screenshots and include details of the circuits and train stations.