Trade-in has nothing to do with Applecare+. AC+ is an extended and expanded warranty service, trade-in is getting value for your old phone to put towards a new one - which model is up to you and you pay the difference.
If you have a better condition phone due to recent replacement, you might get a better trade in value but probably equals out with deductible.
Heavy duty velcro is your friend.
Just put some clear packing tape over the whole back of the phone neatly and trimmed a bit over the sides, just to hold it together so you don’t get shards flaking off everywhere, and leave it in it’s case, until you decide to repair or upgrade or whatever.
Not likely to damage the phone further, more injury to yourself and obviously the phone is not water resistant anymore, so keep it dry.
As mentioned panoramic images can go up to 60+ MP, because images are stitched together horizontally. MP count is relative to image size, so the MP count goes up.
It’s more the quality of the cable really, common fault is internal breakage for example because they use less and poorer quality wire. I’ve rarely had any third party fail due but I buy decent branded but inexpensive ones. I’ve not had an Apple cable fail either, but have had cosmetic damage like a lot of people where the sheathing breaks off etc.