I agree, I think it would be useful to have some sort of “welcome screen” that briefly explains certain aspects of delta chat.
If you want to synchronise a second device the easiest and “safest” way is to import a backup from the first device, if you log in without importing the backup, delta chat will generate a new, different key pair so the two devices will not be “fully compatible”.
I also agree with this, but I do not know how complex it would be to implement such a function.
That option I think is designed more for configuring other clients, other than delta chat, that support autocrypt, so I think it is fine that it is among the advanced options.
The easiest thing to do is to delete the account from the second device and import the backup from the first device