Well, it's actually quite simple, I want my pop cap to be infinite. At the same time I want some limiting factors wich you theoretically can overcome, be it at a huge cost. Meaning that there is a limit at any given point in the game, but that that limit can be increased an infinite amount of times (with an increasing cost). In the end it would be impractical to get that extra unit. Rome doesn't allow for it despite introducing a good system for that game, just not worked out all the way through. However Rome was full with flaws, claiming to be realistic, while horses could jump over a 6 meter pike, bad AI etc.
Then again, I think there should be some rewards for an early strike. For GC, I've been thinking about the possibility of making your victory come in levels, where you gain money by how impressive your victory was (or in some cases your defeat). For example a huge rebel fleet attacks your small Imperial fleet. You win against all odds, the Emperor is pleased and gives you money. Supposed the rebel fleet was completely crushed, the Emperor gives even more money tha he would if some ships got away. Each ship destroyed gives you a small amount of extra money as well, depending on it's type. This last part could be implemented in skirmish as well.