It is highly recommended to replace the key board. On some models you can pop out the individual keys, but it is very hard and risky as to the plastic clips can or will break if not done carefully. If you are not very tech savvy, i highly recommend to take it to a professional to have the keyboard replaced as this requires nearly a complete dissemble of the device/mac.
This sounds like your screen (LCD) cracked. It is very unlikely the cables unplugged because from the factory, the cables have a retaining bracket, which make it difficult to unplug. They would've ripped before they unplugged. I recommend to purchase the DIY kit ifixit.com. Also, since the device has been sitting for three years, i'd recommend to get a new battery as well. iFixit has guides on how to replace everything. Good luck!
This may be the result of the volume down button being either stuck or possibly bad. If its bad, it would need to be replaced as its endless clicking internally as the device is powered on. Hope this helped.
Hello, most commonly, the home button module on the digitizer is not aligned properly. It is important to check the orientation of how the old home button was installed on the old or original digitizer that was removed. If you have aligned it properly, I would highly recommend for you to order a new home button.
Hello Mojo, I am not a maker of this site, however I am an expert in the cellular field and would love to help you with your question. The answer is more than likely Yes, it will still likely be relatively easy to acquire parts for your device. Looking back on a older device called the LG G2 (LG's Flagship model) parts are readily available and accessible. Particularly, most flagship phones by Apple, Samsung, LG, HTC, etc will have parts available due to third party manufacturers. No one can tell the future, however it is very likely.