Ok, on the ships screen you should change the header to say:

Objects built x of y (1000 max)

This will remind all players there's a hard limit.

In games as large as 12x12, as the tutorial server is now, this means out of those 144 galactic sectors, any given player won't effectively be able to colonize and control more that about 10 galactic sectors actively or 20 galactic sectors passively. If you are architecting games so that they end with 7-15 large players at the end, then the cap will support that goal. If that was not your intent, then the cap will harm things.

My fear is this: trader player grows to 10-20 galactic sectors, extracts billions and billions in ore, gets attacked by a player and as an act of vengeance, creates a stack of 1,000 Dreadnaughts that just jumps from system to system. No one can defend against that and no one would be willing to abandon all their ships to create a competing stack of 1,000 Dreadnaughts.

"If you attack me, I am going to abandon my goal to win and just create a stack of 1,000 Dreannaughts to take you out."

We essentially have a nuclear option in the game, which could either help to balance or make endgames totally chaotic and frustrating.

Let's see how this plays out. I'm currently skeptical of the limit.