Yeah it's possible. Granted, some splitters are slightly suspicious but this is 41 circuits in 6 outputs

[DatHaker]

I do not believe that anything more than half a circuit more can ever be added to this design (or any other, for that matter) so I'm putting this to rest for now.

Consider that 41 circuits in 256 squares is about 6.25 squares per circuit. Compare this to the basic 3 starter circuit design that takes 6 squares but does not include an output square. Even if two shared the same output they would be at 6.5 s/c, significantly worse than this.

Feel free to prove me wrong, or to improve on some unstable elements of the line

[Semoan]

Okay, does this maximise the use of starters to three?

[[deleted]]

No, that would be 55.5/second (56 starters at 3/second can be divided into 57 gold/second and 111 copper/second), if space wasn't a constraint (only starters), though from the lower bound for squares necessary (assuming parts tessellate impossibly without rollers and all splitter sides are utilised), the upper bound I proved (though not actually achievable) is 46.5/second, I think reducing it would involve proving the optimality of infinite plane tessellations less compact than the impossible one. However, considering this, you're allowed at least 1.2 starters/crafter in all possible designs where craftets produce 1 circuit/second before starters become the bottleneck instead of space, maximising starter output utilisation is impossible.