There's a reddit thread somewhere that details them. I think the point in stardust is to get your pokemon to those max levels, later in the game, when it matters a bit more.
Yes, the higher level you are the higher the cp cap is for you. I'm level 22 now and have about 120k stardust but can capture anything upto about 700 cp which will evolve into something 1600 cp or so or for stuff that can't evolve I'll be able to capture 1100 cp or so.
All pokemon have a maximum cp value.
There's a reddit thread somewhere that details them. I think the point in stardust is to get your pokemon to those max levels, later in the game, when it matters a bit more.