Tradeports:
Does building extra tradeports on 1 planet benefit?
Let's say I have planet A and B, Is it OK to build 2 tradeports at A and 1 tradeports at B? Or does the tradeports have to be 1 to 1 meaning that 2 on A and 2 on B?
If I have planet A,B,C,D Which of the following options is better?
Building 1 tradeport on each of them? (4 in total)
Building 2 tradeports on only 2 planets with higher population (tax)? (4 in total on only 2 planets)
Broadcastcenter
Let's say there are planet A,B,C planet A,B are mine, C is enemies. (They are in chain form)
I have a broadcast center at planet A and the culture already spreaded pass planet B and is on the way to planet C.
My questions:
By building another broadcast center on planet B, does it speed up the culture spread speed to planet C by 1 time? Does it strengthen the culture influence on planet C?
If I build a second broadcast center on planet A instead of B (meaning that i have 2 broadcast centers on planet A), Is the effect the same with above? (Building 1 on A and 1 on

Hope the questions are clear, and I'm looking foward to the answers
Greetings
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Added:
Another short question, If i build 2 or more broadcastcenters on 1 planet, does the effect stack? regarding culture spread strength, speed, tax income
(ignoring about putting it onto other planets closer to the enemy)