Something to add for the Rebirth tank part. It is really annoying and your machine gun overheats way too fast, so keep your fingers on the grenade buttons (g I believe) to keep shooting them as quickly as you can. You don't have to keep pressing them just hold them down. Fire your machine gun in bursts if you can. If you keep dying at one spot try to change the order you are targeting your enemies. For example right after the first helicopter the 2 guys on my right were doing way more damage than the 5 guys on my left.
Also for Rebirth once you get out of the tank your health regenerates but your suit health does not, which is mentioned in the video before. If you are going for the No Leaks achievement as well (I got it on veteran it isn't that hard) make sure to save and quit as soon as your guy reaches up for his face, that means you're about to die from the gas. If you do it before he drops to the ground and reload your check point it won't take away from your achievement.