Hi there,
For 1, you will need to change the bbpress script to copy the avatars from the folder, and upload them to your Discourse instance. You can check the vbulletin import script for an idea on how that could be achieved, on line 212.
As for 2, that is actually going to be a bit more complicated since Discourse can’t access external websites’ data (like http://www.demo.com). So the best way to achieve that would be to keep the same domain, and make some slight changes to the create_permalinks (line 379) function to support the postname parameter.