Innovation: Echoes of the Past rulebook wrote:
...create supply piles with the following number of cards in each:
2P: 3 Expansion, 6 Base
3P: 4 Expansion, 7 Base
4P: 5 Expansion, 8 Base
5P: 6 Expansion, 9 Base
Also note that each player starts with one expansion and one base card.
As for whether a pile has expansion or base on the top, it's supposed to be random. I usually just cut each deck after it's shuffled.