Well, first I had to look up "au-fait."
1) No worries. Easy to upgrade or down grade, usually. You do have to register, unless you use a hack to get around that. You never have to turn wifi on. I usually register via the desk top app, when I need to do so.
2) Everything you need to know is
here.
I don't use Dropbox with my Kobo. I use Calibre to add, delete, and manage everything.
Since you are used to using Calibre to organize your Sony, you will find it is just as easy with Kobo, although the steps are a little different.