Hi,
1. Yes, by username. There is one issue though – at the moment, if you set min amount to zero for the user, the plugin will ignore it and will use your global min amount (i.e. 250) instead. So would have to enter some very small value, e.g. 0.000001. Fixing this already – I’m thinking about adding “special” value, like -1, for users without min amount at all. Will try to release new plugin version today, in a couple of hours.
2. Yes, you can use the plugin on both sites. You just need to generate a key (in https://wpfactory.com/my-account/downloads/) for your staging site, and when you move to a new site, you just delete the old key/site and generate a new key for the new site.