I still only have 5, and all are at level 23 except for one.
It will take a VERY long time to get my warehouses up high enough to hold the resources to even hold the level 6 stuff.
But, I won’t build a 6th unless all of my colonies are Corruption free. So, NEVER.
You have to play with 5.
I find that marble is a definite need, and if it was the beginning again I’d go Marble, then Wine, then Marble, then Crystal, then Sulfur.
Pillaging can get me all the sulfur, crystal and GOLD I need to buy what I need…