1. There can't be a one click import, because Android's security model means that without root privileges one app can't access another app's database.
In principle if the stock launcher could back up its settings to the shared storage Nova could read that. But (a) I don't think it does, and (b) since different launchers have different options and settings it's implausible that they'd save in the same format, so the Nova developer would have to work out how to interpret each other launcher's backups separately. All just for a starting point, since the reason to use a replacement launcher is to do things the stock one doesn't.
2. Yes. As said previously, nothing in Nova changes anything in the stock launcher.
I fact it's not likely Nova will put icons in random positions: if you are one of the people who fills their screens with icons it's more likely that most of them won't be on the Nova home screen at all (they'll be in the app drawer, of course) and you'll have to re-add them to Nova. By default it will probably only put a few on screens (I keep my screens mostly bare of icons, and would remember if I'd had to sit down and remove hundreds of the things!).