mass-effect-3
The war asset display in the war room on the Normandy shows a graph of the effective military strength I collected so far with a marker at a minimum. There seems to be a minimum amount of EMS I need to get to be able to save the galaxy.
Can I actually fail to gather that minimum amount of EMS? And if it is possible to fail, what happens then when I try to finish the game, do I fail to save the galaxy?
This strategy lets you avoid reapers while still giving you lots of time to get your scans done.
Enter into the system you want to scan, scan twice wherever you want to (I try to be systematic but it's up to you). On your third scan the Reapers will appear, so it's helpful to be near the edge of the system. Before you hit that third scan, look at where you would like to reappear (top, bottom, left, right). Scan and move out of the edge of the system bringing up the galaxy map. If you're reasonably good at avoiding Repears you can probably get a few extra scans in before leaving the system.
Remaining inside the ring, point your ship in the direction you want to re-enter the system. For example to show up next to the Mass Relay you would point your ship right.
You will re-enter far enough away from the reapers to perform more scanning. Repeat this technique until you've completed your scanning. Note that the reapers don't move closer to you while you are examining a planet/etc so you do have time to land and get your probes launched.
This video demonstrates the technique effectively.
Asking which sniper rifle has the highest DPS is kind of a bad question, IMO. The most important question that you should be asking is, "How easy is it to hit successive headshots".
All the damage in the world isn't going to save you if you can't hit jack squat.
The M98 Widow had the highest DPS of any sniper rifle in the last game, and its probably still one of (if not the) best in this game also. The problem with this from a DPS standpoint is that it is single shot / reload.
The Black Widow (available from Spectre Requisitions) does almost the same amount of damage as a Widow, but it can fire multiple times without reloading, meaning it should do superior damage if you're more accurate. (You can also get multiple damage bonuses from cloak if you're fast enough, something impossible with the widow because of the reload).
You should also check out the Javelin, which is found on Rannoch. It's like the Widow, but focused on shields/barriers instead of just armor, which makes it very good for banshees.
Best Answer
The worst possible ending is only stated to be < 1,750 points, which, depending on if you play multiplayer or not, could be hard, or easy to attain.
If you don't play the multiplayer at all, your Galactic Readiness Rating (GRR) will stay at 50%, meaning your War Assets rating will be multiplied by 0.50 to calculate your Effective Military Strategy.
If you have a GRR at, or below 3500, it will be halved and thus be below 1750. It's never going to be possible to be at 0, simply because the main quests give you War Assets.