what do people think is the optimal activation count?

I run Rebels and my lists generally range from 10 to 13 activations. My sons Iden list is 9.

Very interested to hear what people think.

10-11 always feels right. Republic and Separatists have always benn a little smaller due to limitation of different units. There are extremes on either spectrum though.

Ultra competitive folks are going to tell you, that you need 12 and certain units are required ( like 3 sniper units and shoretroopers)

I usually aim for 10-12. 8-9 is doable, but always feels a bit light on activations to me, though as a currently primarily CIS players I have gotten more used to running that many.