回答“iTunes won't detect iPhone”Just because the phone says it's connected by the lightning cable doesn't mean it actually is. I had an iPhone 4s with a similar issue as yours. It ended up being caused by a damaged diode on the mother board.
回答“Can I do a Screen n digi Switch?”As long as the size, model number, and all other specifications are exactly the same, the parts would be the same as well. It comes down to your ability to get the screen and/or LCD removed without damaging either. I've never done an LG tablet specifically but from my experience with tablets from various manufacturers, in most cases it can be done. It really comes down to your skill level and patience. If you rush the removal you will break something, no doubt. Give yourself plenty of time and make sure to find a good tear down video and watch it a few times before attempting anything.
回答“lightning cable charger caught on fire”If the device won't power on there is no way to retrieve the data on it.