1. No. The current plugin pulls from the collection of attachments in the database, not from a certain file or folder on the server. That will be coming in a future version.
2. There's no way to control this just yet. But if you want, you can edit the code directly. The speed of the rotation is controlled in
riw.js on line three. You'll see this line:
setInterval( "slideSwitch()", 5000 );
5000 in this case means 5 seconds. You can change that to whatever you want. 10 seconds would be 10000, for example.