If I were to copy the iCloud locked motherboard’s serial number to a new motherboard with something similar to an QianLi...

There is probably not much of a difference on a plus sized battery since it will still have two points that are attached to the housing, but on a normal sized battery I would replace all the adhesive, as one point of contact dosen’t seem very secure. As a good rule of thumb, put it back the way you found it.

Sounds like the display is damaged. If the internals aren’t damaged, it should be a fairly simple fix. Vervanging iPhone XR scherm iPhone XR Screen

Sounds like the display is not properly connected to the battery. Has your display ever been removed from the device? could have been reinstalled incorrectly.

Yes! There are ways of removing this warning. Using a tool like a iCopy you can copy the original battery’s serial number and put it on a replacement battery. This machine is quite easy to find online (Don’t buy it form Alibaba/Aliexpress.) for a reasonable price for what your getting. Hope this helps!

Check your battery health. (Settings>Battery>Battery Health.) From there check Battery health, Apple considers 80%+ to be optimal. if it is lower than 80%, consider having your battery replaced/replacing it yourself.

If you replace the display your self, Face ID and True Tone will no longer work (Yet another one of Apple’s attempts to deter people from doing it themselves, and paying them high prices do to it instead.) This is because the parts in your phone are paired via serial numbers, meaning removing the original display and replacing it with another one will cause the features associated with that specific part of your device to be unusable. The display and front camera will function normally but you will frequently be reminded by your phone that the display is not a genuine Apple display. There is however there is a work around, using a machine similar to a QianLi iCopy, it is possible to copy the original serial number from the display and put it on your new display, tricking the phone into thinking the new display is the original, meaning Face ID, and true tone will function normally. In short, I would personally fix it myself and use a machine to reprogram the screen making it function normally. If you are...

Yes they are. https://support.quadlockcase.com/hc/en-us/articles/115012741687-Does-the-iPhone-8-8-fit-the-iPhone-7-7-case-

Not entirely sure, but sounds like a issue with the display. If your willing to sped the $$$, maybe try replacing the screen?

I’m not familiar with the iPod classic however you problem seems to be a common one. From what I could find online this is a common problem people come across with their iPod classics after using them for some time. It seems that after sufficient use, the click wheel will simply stop working (in your case, just the play button.) other people have had the entire click wheel stop responding at once. The only solution I have been able to find requires the replacement of the click wheel. Luckily it is fairly easy to find replacement click wheels for iPod classics’. Replacement parts are avalibe here on ifixit (link below, with guides for replacement) but are currently out of stock, it shouldn’t be to hard to find them elsewhere should you not want to wait till the part is restocked. Hope this helps! Link to replacement scroll wheel: iPod Classic Click Wheel Guide links: iPod Classic Click Wheel Button Replacement iPod Classic Click Wheel Replacement