With SE you don't need that much space on Nauvis. You should be targeting 10-30SPM in your first playthru; you will get bottlenecked on extraterrestrial resources as soon as you try to ramp up space science. There are people who beat the game off of a single core drill on Nauvis - what makes this mod take so long is designing all the solutions, rather than waiting for the science to trickle.
Artillery (as well as basically everything from the base game) should be considered early game tech: you will later unlock stuff that would make Palpatine salivate.
If anything, you very suddenly run out of things worth shooting at.
> [...] maybe allow for circuit-controlled timing of when to move into the next cluster.
You can achieve that in the vanilla game by blueprinting the artillery outpost (which would include all the necessary supporting defences, like walls/turrets/roboports/etc). Train rolls in, unloads gun+flamethrower ammo, once ammo buffers are ready set a signal to load ammo into artillery, which will start shooting. Set a timer, every time you load a shell reset it, once timer runs out + there are still shells left - you can set off an alarm that the outpost is done. Use a filtered deconstructor to pick the pieces up and move it all over.
Bonus: use a blueprint deployer (https://mods.factorio.com/mod/recursive-blueprints) to automate the "move to the next sector" part. Check out this guy on Reddit to get some ideas: https://old.reddit.com/user/Drogiwan_Cannobi/submitted/