There currently is a migration tool for v2/v5 to v7, but I haven't tested it in a long time; it's a command-line/manual process and still incomplete with a few things. I know this is something I'm going to have to better address (to make it easier), but from what I remember, almost everything did transfer over. I think that's something I'm going to focus on getting to work better before the full release. There was some potential data loss, mostly with ACARS, because all the different ACARS stored their data in their own formats.
But that's something I'll need help testing.
v7 won't be compatible with smartcars. They had their own API layer and stuff which sat on top of classic.