1 File transfers can be done via apps like localsend, pairdrop/snapdrop (selfhosted, I wouldn’t use the public servers), or simply putting files on a shared server, etc.
2 This is impossible to correctly answer until the new phones are actually out. Reason being we don’t know the restrictions (or hopefully not) that Apple will arbitrarily apply to the port. The iPad, for what it’s worth, can easily mount USB C drives and other accessories, so, hopefully Apple continues in that vein of sanity
3 no
4 my iPhone is my actual phone phone and the pixel is wifi only.