Yes even if you set it to none, installations will begin to pop up as the insurgency builds. Depending on the map and number of civs, I'd say 30 insurgemts is an ok place to start and test for a few hours with.

Over the last few days, every substantial edit I've made to my missions has been lowering the amount of initial installations and insurgents. Currently I have around 85 on Reshmaan (BIG map), 65 on Takistan (probably too many. We'll see) and 50 on FATA (seems ok).

Though obviously if these are one off sessions and not long term persistent, your mileage may vary. I prefer long term persistent (in the vein of British Steel :) ).