I think, as many here, that the number of leaders is quite adequate. My fear is that the leaders will not affect gameplay enough. There isn't a lot differentiating each leader, and the differences will come during the game as you level up your leader, which might in the end turn out too often the same way.
As for the civs, Yes 10 in each age is enough FOR THE PLAYER... and will increase throughout the lifetime of the product, which is perfect. As many have mentioned, the problem is more: Is it enough for THE AI civs, and is seems obvious to me that it's really not, at first, and we will feel we always play against the same civs
for a long while. Again, in time, this will get better as DLC pour in, so all in all I'm quite ok with the numbers for base game... By the time I get to being tired of seeing the same civs as opponents, new ones will have come.