Invest in several colored Sharpie pens. When you see a red circle on the guide, tap that screw head with a red sharpie, orange, green, blue and so forth. This makes it almost fool-proof to not mix up your screws when re-assembling the phone or any other piece of equipment.

Invest in and use some colored Sharpie Pens... I color the tops of the screws orange and red etc. to match the colors of the circles in this guide. Then when I go to put them back in there's no doubt as to which screw is the correct size.

When re-assembling, this is the most difficult cable to re-align and re-connect. A second set of hands is helpful. If not available, be patient and line up the connector carefully. Once reconnected, use care not to 'open' the front cover beyond about 85° to prevent pulling this one back off... If you do, you will have to power-cycle the phone (disconnect the battery) to get things working properly again.

1. With regards to the bent battery, you were right to replace it. LiOn Batteries are very dangerous when the cells inside are compromised. Even though the good ones have circuit breakers built in to prevent fire, they can fail. A LiOn battery - even a small one in an iPhone - can go "high order" and cause a fire that is next to impossible to extinguish. A brief search on YouTube for Lithium Ion Battery fires will quickly convince even the skeptical.

2. The way I keep track of screws... Get a complete set of all colors of Sharpie pens. When disassembling, I touch the screw head with the same color pen as the circle in the iFixit Guide. Then when reassembling I know where the green, orange, red, & blue screws go!

Re-assembly hint: Laying the base, keyboard down, on a table top with the hinge side over the edge about 1/2" toward you is a more stable position for re-assembly than trying to do this up on its edge. This has the added benefit of being able to reinsert the torn screws vertically.