Try replacing the camera and flex assembly.

You can find it on eBay. It is sold along with the two clear plastic pieces.

You will need to replace the flex assembly.

When replacing the battery, be careful not to open the LCD more than 90 degrees. You may have damaged a flex cable assembly or possibly the connector may not be seated correctly, although unless you removed the connector cover, that is unlikely. Or if you had to pry the battery out, you may have damaged something else. Since the cameras are on different connectors it doesn't sound like something simple.

Seems unlikely. The glass is glued to the LCD assembly, and there are no gaps where dust could get under anything. I've heard of people replacing the glass without reglueing it, which could allow dust in. But I'm not sure how dust would get in the phone in the first place.

Use just a dot of B-7000 adhesive at each end. It has a pinpoint applicator that makes it easy to get just the right amount, in just the right place. You don't really need the glue, the speaker will hold it in place as you assemble it if you are careful. Also great for gluing the frame to the glass. (Some replacement frames come with glue already applied. Just heat with your LCD separates machine and it will melt enough to adhere.)

Just Google it. There are a number of manufacturers. Some are available on eBay. There is a nice basic temperature controlled LCD Separator Machine for just $35. Expect to destroy a few LCD assemblies learning how to do it, so practice with some scrap displays.

Try resoldering the flex cable. Otherwise one of the flex PCBs is likely damaged.

Warm the area where battery screw cover is in a stream of hot water from the faucet. Be careful not to get water into the keyboard or keys. The warmth will sometimes expand the aluminum enough to loosen the screw cover. Worked for mine.