You will need to buy an unlocked motherboard. I know in the USA that verizon phones are unlocked after you payed them off completely. If you buy a verizon iPhone 6Plus Motherboard and use it internationally you should be good. (Check the IMEI To make sure it isnt locked first!)
The first generation apple watch (aka. Series 0) is the exact same thing as the Apple Watch Series 1 (which came out with the Series 2 (Second Generation) but with a small processor upgrade compared to the original Apple Watch). So an Apple Watch (1st Generation) screen will work on an Apple Watch Series 1. Now Series 1 and Series 2 Screens are completely different and will not work with each other. And obviously a 38 mm screen won't work on a 42mm screen.
Make sure the cables are not torn or ripped, they can rip pretty easily. If they are damaged purchase a new screen, they're relatively cheep. If they're not damage take the cables out and put them back in again. There is a white line on the cables make sure the white line is parallel to the plastic screen connector. Also make sure the latch on the screen connector is closed.
never herd of the soft click sound, where is that coming from ? bottom speaker, ear speaker or somewhere else inside the phone. Try to restore the iphone to factory settings and if that doesnt work, Try replaceing the battery once more (with a new Battery) and also try the replaceing the charging port aswell.
Some times batterys can be defective and wont accept a charge, Try replaceing the battery once more and give it a shot. Also replace the Magsafe chargerport as well as the chargerport could be bad as well.
The iPhone 6Plus has 3 microphones 1. In the earpiece which is used for voice memos and face time calls 2. One on the back of the phone which records audio for videos 3. On on the bottom of the phone next to the headphone jack to make calls. The fix. Make sure those holes on the bottom of the phone are clean, if they are and you still have the same problem, replace the charger port on the bottom of the phone. The part is fairly cheep.