How do I play with a megacorp?

I finally managed to buy Stellaris on PC with the DLCs after years of playing "ultra vanilla" on console. I finished a few matches and decided to try playing with a nomadic megacorp, it was quite fun and now I tried with a non-nomadic megacorp, and well, I was shocked by the cost of 700-1000 influence to open a single branch.

How can I reduce the cost of influence? I used "free traders" and "artisans Inc." as civs. What other tips do you have? And something off-topic, what's a good configuration for a 600-planet galaxy that runs at 2500? I have an excellent PC and even so, the framerate plummeted in a previous peaceful campaign.

If the text was confusing, I apologize; I'm still learning English.🫠