Many people here are insistent that this is a stealth game, and while it is, there are no penalties for playing it as a shooter.
I would say I have killed at least 90-95% of all the enemies I have encountered, up through Zhao's office. I have yet to purchase any ammo for any weapon, and have an abundance of all ammo types. For every enemy killed, you at least recoup some sort of ammo, and with conservative exploration uncovering weapon lockers, random ammo, etc., there is no need to conserve.
You can play the game utilizing stealth, combat, or a mix of in between, but you will need to hack regardless of which way you primarily play.