All games I have played the AI and I end with a staggering amount of ships- I think there should be a limiting mechanism. Perhaps something similar to Logistics in GalCiv II
The solution for limiting the number of ships would be to raise the price of capital ships. The ships should be so expensive that, even the richest empire could field only a few hundreds capital ships. In history, but also in fiction, fleets are very expensive. For exemple, at Trafalgar, the strength of the two fleets was under 100 capital ships, at Jutland there were about 400 ships (including almost 200 destroyers, torpedo boats and other support ships), today, the most powerful fleet, US Navy has a tottal of 300 ships. In fiction, at the decisive battle of Endor, the total strength of both combatants, in terms of capital ships, was approx. 100 ships or less, with a few hundreds starfigters. Only in Star Trek DS9, the battles are huge, at the battle of caradssia prime, there are over 1000 allied ships, by contrast, at Wolf 359 the Starfleet field only 40 ships.
In conclusion, the ships should be expensive,slow to build but also powerful and with a high surviability. Introduction of a limiting mechanism, like population capacity would hurt the gamplay, because the game would became a rce for building more houses or logistic buildings or what ever they are. I prefer to have 100 ships that can survive, than to have 1000 that die as fast as they are produced.
Sorry for the long post......... and for the bad spelling