NodeBB plans range from $35 to $100, depending on the feature set.
$75 and up plans give you advantages like custom DNS forwarding (so you can use something like mypersonaldomain.com instead of myapp.nodebb.com) and daily backups. All plans come with use of the support ticket system, so you can reach us for support for individual instances.
I suspect there will be a lot of customized stuff that we end up with when we actually do the import (though to be fair, while I think NodeBB is our leading candidate, it's not a done deal yet). We did a partial import from CS to Discourse, so a lot of the user deconfliction has already been worked through.
You can't get the current user data without their uid. If you have access to the express req object you can grab it with req.uid or if it is a socket call then its socket.uid. The value of uid is 0 if the user is not logged in.