Do you experience problems during downloading?
Check your connection in Status and Interface settings window.
Use Test Server in Config > Servers.
We will probably ask you to do a test using only basic settings.
Do you experience problems during repair or unpacking?
Enable +Debug logging in the Status and Interface settings window and share the relevant parts of the log here using [ code ] sections.
Do you mean the "Temporary download folder" or the final folder?
The first one can only have one instance.
Multiple final folders can be set up using the category system.
See: http://wiki.sabnzbd.org/configure-categories