I keep the tax around 30%, take it down a notch if they are growing restless. Played through the game without getting a single revolt.
You can make a lot of money early-ish on by picking up time bombs (before they blow up! ) that drop from enemy agents and selling them for 25k a pop.
The Long Range Rifle is also a very cheap, cost effective alternative to the super expensive Laser that remains useful for the majority of the missions in the game.
Also, skipping the V2 enhancements saves good money early on.