But a starship would have replicators and would fabricate what require. They don't have fuel in any way like we imagine. They don't need supplies.
The idea rather is to impose a limit based on technology, sphere of influence, and based on force projection and starbases.
But even this is largely irrelevant even as early as turn #300, for one doesn't attack the most distant enemy, right? That would be a logistical nightmare and needlessly risk the crew. You attack typically what is closer as whatever is in the borderlands has an extemely high chance of being defenseless unless the opponent is a genius or has a fleet ready to engage probes.
The Omega are using Vi Dreadnoughts as flagships of fleets, but they actually can use a better dreadnought, the Pairos class, but it would slow them down as it's a minor race starship so of limited availability this early in the game.

It is better when designed.
http://birth-of-the-empires.de/wiki/ind ... Delarianer
This is why a campaign editor would be handy as that would be a factor limiting engagements on giant map. The best aspects are probably seldom seen even though they exist.
Think about it, a fleet in which only some ships are cloaked rather gives away the element of surprise. What is equired is an entire cloaked fleet. That would be terrifying as a whole undetectable armada is there ready to pounce.
You would suppose that range limits you when it does not really. The further you attack into an empire, the better the defenses. What you want to do is flank a sprawling empire radiating out and with cloaked ships where they are not expected. Essentially this is what submarines do when they have steath capacity and hypersonic ballistic missiles. No warning and incredible speed and no range equals almost certain lethality.