20 cities by 2000BC

I guess that's one of the reason's I lose to ICS'ers

If I'm lucky, I have 12 to 14 by then...
Monarchy by 3250 or 2850 depending how long it takes me to start my first city. Anything after that, and I know I'm way behind.
The rest are really based on the situation I have to deal with it.
I'll have an early wonder long before 2000 if I have a city with great production. But if not, 2000 seems about right.
Philosphy... it depends whether I think I'm in the hunt to get it first. If I think I have fallen behind, I will take a different path... probably head straight to trade or go the "war" route.
While I like to get to trade asap, sometimes it just doesn't work that way... again, depending on the situation.
So with the exception of Monarchy, I don't really set any firm "date" goals, because everything is really subject to the game I'm playing.