To put your mind at ease I can guarantee where you have the tear will have absolutely no effect on the operation of your phone. The sim tray is directly under this piece and doesn’t require any heatsink I don’t know why they covered it to start with unless it was for cosmetic reasons. If it doesn’t stay down just cut a small bit of double sided tape and stick it back down if you want it to look nice.
As long as it was smoke coming from the battery and not the logic board it should boot up fine. If you have a multimeter you could check the main power rails “PP_BATT_VCC” and “PP_VDD_MAIN” But it won’t hurt the phone by replacing the battery.
You can purchase a home button FPC for a couple of dollars but if you don’t have the equipment and microsoldering experience it will be extremely difficult to do the repair. For an experienced repair shop it would not be a big job and you should get a quote.
The only time I have seen this is when a phone developed phantom touch. As this is an iPhone 6 plus it is a good candidate for this scenario as it is a signature fault. You will not be able to update a disabled phone through iTunes. You can only do a restore. You could try with 3Utools it has an option to restore with users data. You can try this once and it should bring you back to the enter passcode screen. I have tried this on one phone and it didn’t recognise the passcode I put in, and went back to the disabled screen.
It sounds like you have damaged the home button flex. The one coming off the screen that connects to the logic board. Check around the 90 degree bend you might need a magnifying glass but I suspect you will find a microscopic tear. You will need to replace your screen again.
This is a common problem with the iPhone 8 series caused by the ground pins at the end of the home button connector being pushed in. If you have some sort of magnification you should be able to pry them out into their normal position. This is the FPC that your cable in the bottom image connects to
The component missing is an inductor on the main power rail. Unless you removed this yourself I would say your phone has a power rail short probably VCC_MAIN or possibly a charging problem. Obviously someone has been trying to diagnose the problem. You will need a multimeter and some board view software to continue with getting this phone to boot.
You haven’t described your problem properly but if it is only an audio issue it would point to the audio IC. It is a signature fault with this model. If it also has any of the following symptoms it would confirm it. These are the symptoms of audio IC failure on the 7 series. · Callers can't hear you · You can’t hear callers · Voice memos are greyed out · Sound doesn't record on videos · Siri can't hear you · You hear static on calls · Speakerphone doesn't work · Phone takes a very long time to boot The audio IC repair requires microsoldering as jumper wires need to be installed.
Are you using a certified cable? By the sounds of it the charger might not be putting out the correct voltage or maybe the voltage is to dirty. Your phone has two charging IC’s “Hydra” and “Tristar” The Hydra IC lets the Tigris IC know that it can start charging. If the Hydra IC thinks there is a problem with the voltage it will not give Tigris the okay to charge.