I tend to work with two types of harvesters for fuel, first up is the kind that works as a stationary fueling point. These tend to be massive things that get towed into position, packed with huge numbers of storage tanks and set up so they will slowly fill to maximum capacity in 5-10 years or so. In reality they never get full as they are always used by passing ships as fueling points. Second up are my still large but automated fuel miners, these will be designed so that they can fill to maximum capacity in around 3-4 months. They are built with just enough engines to get them to around 200-300km/s, once built they are sent under their own steam to a site where there is also at least one moon in orbit, the moon is set up as a fuel depot and the harvesters given conditional orders that mean they work on a perpetual cycle of filling up and moving to dump the fuel at the depot and return to the site.
I also tend to have small fuel transports that work on repeat cycles between the depots and larger colonies meaning there is always a constant supply flowing in for the shipyards etc. Doing things this way means the only real interaction I have with my fuel industry is by way of updating the harvesters, when I increase my naval ship sizes or go on a large ship number expansion. I then simply do a doubling on ship size for my harvesters, build a new mining fleet and return the old ones for scrap. Other than that the entire fuel operations for my current campaign are all running without any input from me.
