Hello,
For your first question, if you choose to purchase an upgrade with a discount for user who own previous version, you will get a new license key for that new product. Your old product should still be there in your product list and you should be able to use it as usual.
For the second question. From what I understand you will need to install on all system with Multiplicity v4 for it to work. From what I know, you do not need to have another license for your secondary PCs.
Thank you.
Basj,
Stardock Community Assistant.
