Question

On how many computers, I can activate Sphere subscription, when I got 1-year free members ship?

Answer 1

Sphere subscription isn't tied to a computer as it is a service.

Within that service exists the applications, add-ons, soundpacks and other resources which you gain access to based on your monthly payment.

The products you choose to install from the sphere will have their standard activation terms however, for example with Studio One you get 5 activations, whereas Melodyne Essentials 5 is limited to 2.  But you are free to manage those activations.