Ok. If you read my full post I have you test all 3 microphones without your headphones plugged it. Try all three and post the results.

Sorry to hear about your touch ID on your iPhone. A couple of questions to help you. 1.Do you transfer the backplate with fingerprint extension cable from the old LCD assembly to the new LCD assembly? If you did, there is a good chance that the backplate with fingerprint extension cable is bad is often the case with ones that are not the original apple fingerprint extension cable. 2. There is a good chance there is a tear in the fingerprint extension cable or that one of the connections is bent. You can post a picture of both the female and male connectors to the home button and fingerprint flex cable and I can take a quick look. If the fingerprint extension cable is broken you can buy one from ifixit. 3. Worst case scenario is that you have a small tear on your home button flex cable and you will never be able to have your fingerprint work again unless you can get apple to replace the screen for you which most likely they won't. You can purchase a new home button from ifixit or maybe your local repair...

So to start off with, at least you headphone jack is working and not stuck in headphone mode which can be a P.I.A. I know this is possible because I have a audio jack I take phone calls with with my car and people can hear me through one of the 3 microphones. 1. Let's test to make sure all of your microphones are working. Take two quick video and say test or something on both the front and rear camera. Playback and confirm you have sound. 2. If you haven't deleted it with the new IOS, go into voice memo and click the upper right corner of the screen with the sound icon, it's a little buggy since IOS 10 so toggle it from blue to white a couple of times to make sure its recording on your lower microphone and test the lower microphone by making a recording. If all three of your microphones work than we can go from there. Let me know the results!

What type of iPad is it. How are you turning it on once it's off. There are a couple of solutions and workarounds for this.

You probably did not re-seat all the LCD connector probably or there is some type of debris between the connectors. You also could have damaged the area. If you want to take a picture of the connectors and post it here I could possibly help.

The phone doesn't have to be plugged in to update it. I think it just needs to be over a percentage to upgrade. What kind of cable are you using? Has the phone ever been worked on before, are all of the parts in the phone apple original? You could always try doing a DFU restore but you need to make sure you have a good cable to connect to iTunes. Are you using a MFI certified cable, or can you get one?

There already are iPhone 6s screens, they seem to have a going rate of $280 plus dollars. Remember with labor it will probably be over $300 dollars. You may want to point people to apple who may or may not have replacement parts. If they don't you can do a out of warranty replacement for $300 dollars.

I actually wouldn't change the battery until you say what kind of phone you are using. Do you mind updating up on the type of phone you are using. If it is a iPhone 5 series or greater, are you using mfi certified cables?

The best way would be a ultrasonic cleaner with some type of cleaner like Brandon electronic cleaner. If not alcohol will help but won't really clean.

Also to follow up with what Jessa said, there is a small filter that people rarely transfer over from the old device to the new device. Most of the time it isn't needed but I suppose that apple puts it there for a reason. I've seen lots of proximity filters fail when people do not handle them with care and force them into the bracket they lie in. The iPhone 6 seems to be the best iPhone yet that makes it easy to seat the sensor.