Hello,
I believe its 1 + 4, to get more you will need Multiplicity 4 Business edition. But, to be sure, I have forwarded your problem/question to Stardock Support Team for their assistance. Please keep an eye on this thread for any updates.
Yes there is discount offered for Multiplicity 3 Pro to Multiplicity 4 Pro, just need to click on the "upgrade" button to check for the discount eligibility.
Thank you.
Basj,
Stardock Community Assistant.