Hello,
Let me try to answer your questions.
- I believe you will need to have Multiplicity 4 Pro for what you trying to do. Its has KVM mode (Control multiple PC's with one keyboard, mouse and monitor) Up to 5 PC KVM. If you purchase the base version (Multiplicity 4) you only have KM mode, which mean there will be no monitor sharing, to make these work, you will need to be able to see the monitor of the connected PC.
- The is no subscription for Multiplicity 4 Pro.
As a reference:

Thank you.
Basj,
Stardock Community Assistant.